(2) Atom is the name of an XML-based Web content and metadata syndication format, and an application-level protocol for publishing and editing Web resources belonging to periodically updated Web sites. All Atom feeds must be well-formed XML documents, and are identified with the application/atom+xml media type. [Source: AtomEnabled]

IETF AtomPub Working Group
The goal for the working group is to produce a single feed format and a single editing protocol; the working group will only consider additional formats or additional protocols if those charter changes are approved by the IESG.

MPLS AToM: Transport, Platform, and Release Specifics
The AToM documentation set describes the AToM features and explains how to implement them.

The Atom Publishing Protocol
The Atom Publishing Protocol is an application-level protocol for publishing and editing Web resources belonging to periodically updated websites. The protocol at its core is the HTTP transport of Atom-formatted representations. The Atom format is documented in the Atom Syndication Format.