A Twitter chat is a twitter-based public discussion based on a specific topic. Twitter chats can range from half an hour to an hour long.

Pre-written questions act as discussion prompts, so the length depends on how many prompts there are. The prompts are tweeted using a hashtag, so participants can follow the discussion and participate if they wish.

Twitter chats are live, so people wanting to participate in the chat meet at a specific time.

Twitter Business discusses how Twitter chats can improve your audience engagement strategy here.