1. In networking, a token refers to a series of bits that circulate on a token-ring network. When one of the systems on the network has the "token," it can send information to the other computers. Since there is only one token for each token-ring network, only one computer at a time can send data.

2. In programming, a token is a single element of a programming language. Some examples of programming tokens are reserved words, punctuation marks, and operators (i.e. +,-,*,/).

3. In security systems, a token is small card that displays an ID code which can be used to log into a network. The card user enters a password which causes the card to display the current ID needed to log into the network. The token adds an extra security level to the network because the IDs change every five minutes or so.