Crossposting is the act of posting verbatim copies of one message on multiple message centers, without customising each copy to suit the audience or forum.

The practice likely originated on Usenet newsgroups where individuals seeking replies, an answer to a technical question perhaps, would post the query to related newsgroups. Most Usenet software would store the article only once, with symbolic links to all the other locations. Usenet is a distributed Internet discussion system that evolved from a general purpose UUCP network of the same name. ... A symbolic link (often symlink, especially in verb form, or soft link) is a special type of file in a Unix (or Unix-like) filesystem that allows a file entry to refer to another directory entry. ...

Presently, the crossposting can mean posting verbatim text to a number of blogs, sites like Slashdot, or carbon copying the message to a number of mailing lists. Slashdot (frequently abbreviated as /.) is a popular technology-related website, updated many times daily with articles that are short summaries of stories on other websites with links to the stories, and provisions for readers to comment on the story. ... Carbon copying, often abbreviated to c. ...

A second meaning has evolved on some internet message boards. Crossposting or also known as x-posting is used to describe that you started typing a response, while in the meantime others submitted, invisibly to you, a posting containing approximately the same message you have posted or render your response inappropriate.

Crossposting is a technique used in Astroturfing to generate the appearance of wide-spread support. In American politics and advertising, the term astroturfing pejoratively describes formal public relations projects which deliberately seek to engineer the impression of spontaneous public reactions to a politician or political grouping, product, service, event, etc. ...