Tag
In web terms: Notifications or commands written into a web document. (See HTML Tags)

TCP (Transmission Control Protocol)
See TCP/IP.

TCP/IP (Transmission Control Protocol / Internet Protocol)
A collection of Internet communication protocols between two computers. The TCP protocol is responsible for an error free connection between two computers, while the IP protocol is responsible for the data packets sent over the network.

TCP/IP Address
See IP Address.

TCP/IP Packet
A "packet" of data sent over a TCP/IP network. (data sent over the Internet is broken down into small "packets" from 40 to 32000 bytes long).

Trojan Horse
Computer program hidden in another computer program with the purpose of  destroying software or collecting information about the use of the computer.