In the
Jabber open-source
instant messaging system, indicates a relationship between two users involving the transfer of
presence information. If Alice subscribes to Bob, Alice will receive
presence messages from Bob indicating Bob's current status. Subscriptions are frequently
bidirectional (e.g. Bob subscribes to Alice as well), but need not be.
Subscriptions are managed by using <presence/> elements with a "type=" attribute of "subscribe" (to request a new subscription), "subscribed" (to acknowledge a new subscription), "unsubscribe" (to request the removal of a subscription) or "unsubscribed" (to acknowledge the subscription's removal). Subscription information is also stored as a "subscription=" attribute on roster items for a user.
In online discussion or code, the term "subscription" is often abbreviated "S10N".