| Word | Description |
| TCP/IP | An acronym for 'Transmission Control Protocol/Internet Protocol'. TCP/IP is a set of rules that establish the way data is transmitted over the Internet between two or more computers. TCP/IP is the standard protocol upon which the Internet relies. |
| Telco (telecommunications organisation) | Generally linked with electronic commerce through the provision of e-commerce-enabling hardware and/or software. |
| Terminal | The term 'terminal' has several uses. It is sometimes used to refer to any computer connected to a network. It can also be used to refer to a device, usually at least a keyboard and a screen, which allows you to send commands to a computer. |
| Thumbprint | A hash value that generates or verifies digital signatures. |
| Token Ring | Refers to a type of local area network (LAN) where hardware is connected in a ring or star layout. A particular method of passing information from one computer to another is used. This ’token passing‘ scheme ensures information is passed efficiently between computers. |
| Trap door | A deliberate hole built in to a computer program, which can be used to gain unauthorised access to a computer or network. |
| Trojan | Named after the Trojan horse used by the rescuers of Helen of Troy. A Trojan is a computer program that disguises itself as a useful software application that is actually used to gain access to your computer. |