Topics are called topics because the original post and its replies generally contain just one topic of discussion. For this reason diverting from the original topic being discussed is rude and considered "stealing" or "hijacking" the topic. The topic starter usually defines what is and isn't "on topic."

In many cases, the topic's starter (the member who made the first post) is considered to be the "owner" of the topic. Topic starters can be given elevated permissions within the topics they start.

Polls and calendar events can be tied to topics, and topics can be made sticky or locked. Topics are always posted within a certain board, and are subject to various forms of moderation.

By default the number of topics is limited to 16,777,216.