An instant messenger is a computer application which allows instant text communication through a network such as the Internet. An instant messenger is a client which hooks up to an instant messaging service. Instant messaging differs from email in that conversations over instant messaging media happen in real-time. Generally, both parties in the conversation see each line of text right after it is typed (line-by-line), thus making it more like a telephone conversation than exchanging letters. Instant messaging applications may also include the ability to post an away message, the equivalent of the message on a telephone answering machine.
Popular instant messaging services on the public Internet include Jabber, AOL Instant Messenger, Yahoo! Messenger, .NET Messenger Service, and ICQ. These services owe many ideas to an older (and still popular) medium known as Internet Relay Chat (IRC).
Instant messaging has arisen in parallel in many places, and each application has its own protocols. This has led to users running many instant messaging applications simultaneously to be available on several networks.
Alternatively, some instant messaging applications attempt to cover all standards in a single client. Examples include Trillian and Jabber.
There have been several attempts to create a unified standard for instant messaging: IETF's SIP (Session Initiation Protocol) and SIMPLE (SIP for Instant Messaging and Presence Leverage), Apex (Application Exchange Core[?]) and Prim (Presence and Instant Messaging Protocol[?]), XMPP (Extensible Messaging and Presence Protocol).
On December 19, 2002, AOL Time Warner announced that they had been issued a United States patent for instant messaging, but they also said that they had no plans on enforcing their patent at the present time.
