Typically, the newsgroup is focused on a particular topic of interest. A message sent for publication on a newsgroup is called a "post". Some newsgroups allow posts on a wide variety of themes, regarding anything a member chooses to discuss as on-topic, while others keep more strictly to their particular subject, frowning on off-topic posts. The news admin (the administrator of a news server) decides how long posts are kept on their server before being expired (deleted), which is called retention. Different servers will have different retention times for the same newsgroup; some may keep posts for as little as one or two weeks, others may hold them for many years.