A form of technology that detects and announces when a user
connects to the net
using some sort of a computing device.
The most common example of "presence technology" is instant messaging. When you log on to an IM service, your connectivity is immediately announced to your "buddy list".
Currently, Internet engineers are working on a way to develop presence technology so that the announcement of a users' connection to the network can be universal and can extend to other network services besides what the user is currently using.