"ATOM" can refer to different things depending on the context. In the case of talking about the internet, it refers to a standard web feed format used for syndicating and publishing web content (Web Feed Format). It is often used for blogs and news websites to provide a machine-readable format of their content, allowing users to subscribe to updates using feed readers.

Web feed is also known as the Syndicate feed or News feed. Aggregation is used to access a collection of web feeds so that the user can collect all the information in one spot. Web feeds use Pull technology to support the user in receiving updated content.

Two major Web feed formats are RSS and Atom. Expansion of RSS is Really Simple Syndication and is sometimes expanded as Rich Site Summery.

References: https://www.engineersgarage.com/web-feeds/