Wikipedia
Webmention
Webmention is a simple protocol to notify any URL when a website links to it, and for web pages to request notifications when somebody links to them. Webmention was originally developed in the IndieWebCamp community and published as a W3C working draft on 2016-01-12. Webmention enables authors to keep track of who is linking to, referring to, or commenting on their articles. By incorporating such comments from other sites, sites themselves provide federated commenting functionality.
Similar to pingback, Webmention is one of four types of linkbacks, but was designed to be simpler than the XML-RPC protocol that pingback relies upon, by instead only using HTTP and x-www-urlencoded content.