Ban (law)
A ban is, generally, any decree that prohibits something.
Bans are formed for the prohibition of activities within a certain political territory. Some see this as a negative act (equating it to a form of censorship or discrimination) and others see it as maintaining the "status quo". Bans in commerce are referred to as embargos.
See also: List of banned books.
Internet
Ban means barring access to specific network resources for a specific user either indefinitely or for a specific time period. Typically, a ban is levied by the administrators of the resource as punishment for abuse or attempts to abuse the resource, compromising its free use by others. Most resources have a policy (Terms of service) that outlines what behavior is prohibited and when and how a user will be banned.