Glossary of Private Investigation Terms
Whether you are hiring a private investigator for the first time, studying for a PI exam, or just curious about the profession, this glossary covers the terminology you will encounter. Every definition comes with practical context about how the term is actually used in the field.
A
Affidavit: A written statement made under oath. Investigators prepare affidavits to formally present their findings as sworn testimony. These documents are commonly used in court proceedings, insurance claims, and legal depositions.
Asset Search: An investigation to identify and locate a subject's assets including real estate, bank accounts, vehicles, investments, business interests, and other property. Commonly requested during divorce proceedings, debt collection, and pre-litigation research.
Auto Surveillance: Following a subject in a vehicle. This is one of the most common types of mobile surveillance and requires knowledge of driving patterns, traffic flow, and techniques to avoid detection while maintaining visual contact.
B
Background Check: A comprehensive investigation into a person's history including criminal records, employment history, education verification, credit history, and public records. PI background checks go far beyond automated online database searches.
BOLO: Be On the Lookout. An alert distributed to law enforcement or investigation teams to watch for a specific person, vehicle, or item. Used when a subject is expected to appear at a particular location or area.
Bug: A hidden electronic listening device used to intercept conversations. Also called a wire. The use and detection of bugs falls under TSCM services.
Burned: When an investigator's cover is blown or the subject becomes aware of the surveillance. Once burned, the operation is typically compromised.
C
Canvassing: Systematically interviewing people in a specific area to gather information about an incident, subject, or situation. Door-to-door canvassing of a neighborhood is common in missing person and witness identification cases.
Chain of Custody: The documented record of everyone who handled a piece of evidence from collection through court presentation. An unbroken chain proves the evidence was not tampered with.
Covert: Done secretly. Covert surveillance means the subject does not know they are being observed. The opposite is overt (open, visible) investigation.
Counter-Surveillance: Techniques used to detect whether a person is being surveilled. A counter-surveillance sweep checks for people following the client, hidden cameras, listening devices, and GPS trackers.
D
Deposition: A sworn, out-of-court testimony taken before trial. Investigators may be deposed to testify about their investigation methods, findings, and evidence.
Due Diligence: A comprehensive investigation conducted before a business transaction, partnership, or major decision. Verifies that the people and entities involved are legitimate and that no hidden risks exist.
Dumpster Diving: Searching through discarded trash for evidence. In most US jurisdictions, trash placed at the curb for collection is considered abandoned property and can be legally searched without a warrant.
E-F
EXIF Data: Metadata embedded in digital photos that can include GPS coordinates, date/time stamps, device model, and camera settings. Investigators use EXIF data to verify when and where photos were taken.
FOIA: Freedom of Information Act. A federal law that gives the public the right to request access to records from any federal agency. State-level equivalents exist under different names.
Forensics: The application of scientific methods to investigation. Digital forensics examines computers and devices. Forensic accounting analyzes financial records. Physical forensics examines crime scenes and physical evidence.
G-I
GPS Tracking: Using Global Positioning System devices to monitor the real-time location and movement of a vehicle or asset. Legality varies significantly by state.
Gumshoe: Classic slang for a private investigator or detective. The term originated in the early 1900s, referring to the rubber-soled shoes that allowed detectives to walk quietly.
Intelligence: Information that has been collected, analyzed, and interpreted to support investigation objectives. Raw data becomes intelligence when it is processed and contextualized.
IR (Infrared): Light invisible to the human eye, used in night vision cameras and surveillance equipment. IR illuminators light a scene without alerting subjects.
L-M
Locate: To find a person's current address, phone number, or physical location. Also called a "people locate" or "person locate."
Mobile Surveillance: Following a subject as they move between locations. Requires advanced driving skills, knowledge of the area, and often multiple investigators to maintain coverage without detection.
N-O
NLJD: Non-Linear Junction Detector. A device that finds hidden electronics even when they are powered off. Used in professional TSCM sweeps.
OSINT: Open Source Intelligence. Information gathered from publicly available sources. See our complete OSINT tools guide.
P-R
Paper Trail: The collection of documents, records, and financial transactions that track a person's or organization's activities over time.
Pretext: A fabricated scenario or reason used to obtain information without revealing the true purpose of the inquiry. Legal boundaries apply.
Process Serving: The legal delivery of court documents to a party involved in legal proceedings. Must be performed according to specific state rules.
Retainer: An upfront payment made to an investigator before work begins. The retainer is drawn down as hours are worked and expenses are incurred. Learn more about PI costs and fee structures.
RF Detector: Radio Frequency detector. A device that scans for wireless transmissions from hidden cameras, audio bugs, and GPS trackers.
S
Skip Tracing: The process of locating a person who has left their known address. Used for finding debtors, missing persons, witnesses, and people avoiding legal service.
Stakeout: Waiting and watching at a fixed location to observe a subject or specific activity. A type of stationary surveillance.
Subject: The individual, business, or entity being investigated. Professional terminology avoids using "target" because it carries aggressive connotations.
Subpoena: A legal order compelling a person to testify or produce documents. Investigators may serve subpoenas or be subpoenaed to testify about their findings.
Surveillance: The systematic observation and documentation of a subject's activities. See our complete surveillance guide.
T-Z
Tail: Informal term for following a subject discreetly. "I was tailing the subject from the office to the restaurant."
The Set: The location where a surveillance operation is being conducted. "I am on the set" means the investigator is in position.
TSCM: Technical Surveillance Countermeasures. The process of detecting hidden surveillance devices. See our TSCM services page.
Undercover: Posing as someone else to gather information without revealing one's identity as an investigator.
Witness Locate: Finding and identifying witnesses to an event who may provide testimony or statements for legal proceedings.
Why Investigation Terminology Matters
Precise language is not just professional habit in the investigation industry. It has real consequences. In court proceedings, the difference between saying a subject was "observed" versus "seen" can affect how a judge evaluates testimony. Investigation reports that use proper terminology are taken more seriously by attorneys, insurance companies, and courts.
When you hire a private investigator, understanding these terms helps you communicate clearly about what you need. A client who says "I need a background check" may actually need a full due diligence investigation, or they might only need a basic records search. Knowing the distinction saves time and money.
For aspiring investigators studying for their PI license exam, these terms appear regularly on state licensing tests. Understanding them in context, not just as definitions, is what separates someone who passes the test from someone who actually succeeds in the field.
Terms That Confuse Clients Most Often
Based on our experience working with hundreds of clients, certain terms cause the most confusion:
- Surveillance vs. stalking. Professional, legal surveillance is conducted within the boundaries of the law by a licensed investigator for a legitimate purpose. Stalking is illegal. The key difference is legality, purpose, and licensing. If someone tells you surveillance is the same as stalking, they do not understand the law.
- Retainer vs. total cost. A retainer is an advance deposit, not the total price of an investigation. If your PI requires a $2,000 retainer, that does not mean the investigation costs $2,000. It means they will begin work using those funds and bill additional time as needed. Review our PI cost guide for full pricing details.
- Legal vs. admissible. Something can be legally obtained but still not admissible in court. Admissibility depends on how evidence was collected, chain of custody, and whether it meets the rules of evidence in your jurisdiction. A good PI knows the difference and collects evidence with admissibility in mind from the start.
- Public record vs. publicly available. A public record is an official government document available by law. Publicly available information includes anything posted online or accessible without restricted access. Social media posts are publicly available but are not public records. The legal protections and uses are different.
We update this glossary regularly as new tools and techniques enter the industry. Digital forensics, drone surveillance, and AI-powered research tools are introducing new vocabulary that will appear in future editions. Bookmark this page and check back periodically for additions.
This glossary covers the terms you are most likely to encounter when working with a private investigator or studying the profession. For more information about investigation services, explore our services page or contact us with questions.
Modern Investigation Terminology
As investigation work evolves with technology, new terms enter the professional vocabulary. Digital forensics describes the recovery and analysis of data from electronic devices like smartphones, computers, and cloud storage. Social media intelligence, sometimes called SOCMINT, refers to the systematic collection and analysis of information from social networking platforms.
Geofencing involves creating a virtual geographic boundary and monitoring when a device enters or exits that area. Open source intelligence (OSINT) encompasses any information gathered from publicly available sources. Dark web monitoring tracks activity on encrypted networks where illegal transactions and communications often occur.
Understanding these terms helps clients communicate more effectively with their investigators and better understand the methods being used in their case. As technology continues to advance, the investigation profession adapts its methods and terminology to keep pace with how people communicate, transact, and interact in the digital world.
Investigation Terms FAQ
Burned means the subject has become aware that they are being surveilled. Once an investigator is burned, the surveillance operation is typically compromised and must be suspended or handed off to a different investigator with a different vehicle. Getting burned can happen through poor technique, too-close following, or the subject being naturally surveillance-aware.
Skip tracing is the process of locating a person who has "skipped" or left their known location. This could be a debtor who owes money, a witness needed for court, a missing family member, or a person avoiding legal service. Investigators use database searches, public records, social media research, and field interviews to track down the subject.
Surveillance is the broader term for systematically observing a subject, which can be stationary or mobile. A stakeout specifically refers to waiting at a fixed location to observe a particular place or person. Think of it this way: a stakeout is one type of surveillance. All stakeouts are surveillance, but not all surveillance is a stakeout.
TSCM stands for Technical Surveillance Countermeasures. It refers to the process of detecting and neutralizing electronic surveillance devices like hidden cameras, audio bugs, GPS trackers, and phone tapping equipment. TSCM sweeps use specialized equipment including RF detectors, non-linear junction detectors, and spectrum analyzers.
A pretext is a fabricated scenario or identity used to obtain information without revealing that an investigation is underway. For example, an investigator might call a business pretending to verify employment for a loan application. Pretexting is legal in many situations but restricted by laws like the Gramm-Leach-Bliley Act for obtaining financial records.
Chain of custody is the documented trail showing who collected, handled, stored, and transferred a piece of evidence from the moment it was gathered until it is presented in court. An unbroken chain of custody proves the evidence was not tampered with. If the chain is broken, the evidence may be ruled inadmissible.
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