Definition: instant messaging

Exchanging text messages in real time between two or more people logged into an instant messaging (IM) service. Unlike email, messages are sent immediately, whereas email can be queued up in a mail server for seconds or minutes. However, there is no elaborate page layout: type a brief message and press Enter. Some IM services provide video calling, file sharing and PC-to-phone calling and allow users to switch back and forth. See text messaging vs. instant messaging.

Contact List (Buddy List)
To use instant messaging, people add the usernames of the friends and colleagues they want to communicate with. After logging in to the IM service, everyone in their list may be alerted providing they allow notifications. Each system has its own method for blocking incoming messages.

The IM Services
Instant messaging (IM) became popular after Israeli-based ICQ debuted in 1996, which was later acquired by AOL. There are more than three dozen IM services, and WhatsApp, Facebook Messenger, WeChat, TenCent QQ, Line, Telegram, Skype and Snapchat are some of the largest.

IM programs initially connected only to members of the same service. However, IM clients such as Trillian and Simple Instant Messenger were designed to interface with multiple IM services. XMPP and Matrix are open protocols for instant messaging (see Jabber, XMPP and Matrix protocol).

Short and Sweet

This is a typical IM interaction using the earlier Google Talk service. The user's picture can be real or selected from a list (see avatar). Google Talk was replaced (see Google Chat).