TAO - (Office of) Tailored Access Operations. A cyber-warfare intelligence-gathering unit of the National Security Agency (NSA). 

TARGET - The subject of surveillance.

TARGETING - The process of searching for potential spies. Determining who is in a position to access information and influence, and how to make contact with them.

TECHINT - Technical Intelligence. Analysis of fielded equipment for training, research, and the development of new weapons and equipment for eventual intelligence use.

TERMINATED - Murdered.

THE COMPANY - An unofficial term for the CIA popularized by fiction.

THE TAKE - Information gathered by intelligence collection operations.

THERMAL IMAGER - A heat-sensitive surveillance video camera and display.

THROWAWAY - An agent considered to be expendable.

TIMED DROP - A dead drop that will be retrieved by a recipient after a set time period.

TOKYO SPY RING (the) - Established by the Soviet Union as a means of determining Japanese diplomatic and military intent towards the Soviet Union during World War II.

TRADECRAFT - The methods developed by intelligence operatives to conduct their operations.

TRAFFIC ANALYSIS - Methods for gaining intelligence from the patterns and volumes of messages gathered by communications intercepts.

TRIADS - Asian organized crime gangs.

TRIGGER - A surveillance operative who is watching the target's vacant vehicle, home, garage, office, restaurant etc. and who alerts the rest of the surveillance team when the target is spotted.

TUPAMAROS - An underground group in Uruguay.

TURNCOAT - Person which switch sides, allegiance.