Instant messaging, often shortened to IM or IM'ing, is the exchange of near-real-time messages through a standalone application or embedded software. Unlike chatrooms with many users engaging in multiple and overlapping conversations, IM sessions usually take place between two users in a private, back-and-forth style of communication.
A core feature of many instant messenger clients is the ability to see whether a friend or co-worker is online and connected through the selected service -- a capability known as presence. As the technology has evolved, many IM clients have added support for features such as file transfer and image sharing within an IM session.
Instant messaging differs from email in the immediacy of the message exchange. IM also tends to be session-based, having a start and an end. Because IM is intended to mimic in-person conversations, individual messages are often brief. Email, on the other hand, usually reflects a longer-form, letter writing style.
