Moderation is the act of limiting communication according to some ideas or rules. It can be implemented in advance, preventing unwanted communication, by restricting who can communicate, or where they can communicate. It can also be implemented in hindsight by partially or completely removing messages or content that was already produced.
Moderation can be performed automatically in advance according to metadata known about users and specific places they might communicate. It can be performed automatically afterward by applying rules regarding censored words or phrases. It can also be performed manually by the administrators or management of a communication environment, or by the community around that environment.
Moderation can completely prevent certain communication from passing, or it can change the nature of communication to require recipients to opt-in or have achieved certain requirements prior to reception.