1. One of the meaningful units (names, constants, reserved words, etc.) in the input to a compiler. The lexical analyser breaks up the input, which is a stream of characters, into a sequence of tokens.

2. A unique sequence of bits granting send permission on a network. See token bus, token ring.

3. See Petri net.

4. (security token) A device that, employed together with something that a user knows (e.g. a password), will enable authorized access to a computer system or network. The device may be physical, in which case it is a hard token (e.g. a smart card); or it may be logical, in which case it is a soft token.