In Zulip, streams determine who gets a message. Topics tell you what the
message is about.

Topics are light-weight subjects, very similar to the subject line of an email.
Like in email or a forum, messages about the same topic are shown together as a
conversational thread. Here is what it looks like in Zulip.

![Streams and topics](/static/images/help/streams-and-topics.png)

Topics are one of the most wonderful aspects of using Zulip:

* Lots of conversations can happen in the same stream at the same time, each in
  its own topic. You never have to worry about interrupting — each conversation
  has its own space.
* Conversations can last many hours or days, letting everyone respond in their
  own time. Don't worry about replying long after a message is sent —
  everyone will see your reply in context.

Check out [Why Zulip](/why-zulip/) to learn more about how Zulip's topic model
helps transform how your organization communicates.