In instant messaging (IM) applications on a personal computer (PC), or on a cellular telephone with text display, a buddy list is a list of people a user wants to keep track of. A buddy list can be used to see who is offline, who is online, who is online but away from their computer, who has their phone turned off, who has their phone turned on, or who is currently talking on their phone.
When the user launches their instant messaging application, it connects to the instant messaging server, logs the user on, and displays the screen names of people the user has put on their buddy list. The server checks the user's buddy list and visually lets the user know which buddies are available for messaging. At the same time, the server updates the buddy lists of the user's buddies to indicate that the user is currently available for messaging.
With some instant messaging applications, it's possible to store a message on the instant messaging server temporarily if a buddy is unavailable, so that when the buddy does become available, the message will be sent.