TrackBack is a technical specification for an Internet program that lets a blogger know when another blogger has commented upon one of his posts.
The TrackBack specification describes a REST framework, within which the client makes a standard HTTP call, or ping, and receives an XML response. The ping is automatically generated in some versions of blogging software, though in others a blogger has to manually send the ping. Software that supports the protocol will display a TrackBack URL at the end of each post.
A TrackBack list on a blog may display summaries of all of the content with links to that blog or a specific post, listed in chronological order. This mechanism makes it easy for a reader to quickly follow an online conversation that spans multiple blogs. TrackBacks can be used in a variety of other ways beyond simple links to posts citing the original content. For instance, a blogger can use TrackBack to inform other bloggers of related resources or to create an archive of information related to a particular topic.
TrackBack was originally implemented during 2002 in Movable Type, a blogging software product distributed by SixApart. It was widely implemented in TypePad, WordPress, LiveJournal, which are all SixApart products. SixApart has submitted TrackBack to the IETF for approval as a standard online protocol. While Google's Blogger notably has not incorporated TrackBack, a recent beta release that included "backlink" essentially duplicates its functionality.
TrackBack has been targeted by spammers hoping to improve search engine rankings to their own sites by increasing their number of inbound links. Many versions of blogging software have added spam filters, such as CAPTCHAs, to block link abuse.