Definition - What does Presence mean?
Presence is a service that stores, accepts and distributes information on whether someone is available to communicate over a network. Presence service can be applied as a single server or have an internal structure involving multiple servers and proxies.
Presence may also be referred to as presence informatin.
Techopedia explains Presence
The most common example of presence is the status messages presented for users in an instant messaging system, which may read "available", "busy", "offline" or "out to lunch", among other statuses. This indicates a user's current communication status. Presence is often set by the user, but can also be used by technology to infer the user's state. As such, comprehensive presence information that integrates various technologies (such as the person's calendar and mobile devices) can have privacy issues.