Asynchronous Transfer Mode
(ATM, or "fast packet", "Asynchronous Transfer Mode Protocol", ATMP) A network protocol that dynamically allocates bandwidth between incoming channels and multiplexes them onto a stream of fixed 53-byte packets (called "cells"). A fixed-size packet simplifies switching and multiplexing. ATM is a connection-oriented protocol. It can use different physical layer transports including SONET, DS3, fiber or twisted pair.
The ATM Forum is one of the main bodies promoting ATM.
Wideband ATM is an enhancement.