# About streams and topics

In Zulip, conversations are organized by conversation **streams** and
**topics**.

## About streams
On Zulip, users communicate with each other in group chats by sending messages
to streams, which are similar to conversation threads.

Streams are either:

* **Public** - Public streams are for open discussions. All users can subscribe
to public streams and discuss topics there. Any Zulip user can join any public
stream in the realm, and they can view the complete message history of any
public stream without joining the stream.
* **Private** - Private streams are for confidential discussions and are only
visible to users who've been invited to subscribe to them. Users who are not
members of a private stream cannot subscribe to the stream, and they also cannot
read or send messages to the stream.

Users are subscribed to specific streams in the realm by default, such as the
[#announce](the-announce-stream) stream. Users can easily
[view messages](/help/view-messages-from-a-stream) from a specific stream; in
addition, they can [browse](/help/browse-and-join-streams#browse-streams) their
stream subscriptions using the Zulip stream browser.

If they wish to read messages from a stream that they're not subscribed to,
users can choose to [join](/help/browse-and-join-streams#subscribing-to-streams)
a stream. Similarly, if they are not interested in the topics being discussed in
a stream, users can choose to [unsubscribe](/help/unsubscribe-from-a-stream) from a
stream.

Users can also customize their stream settings; they can
[pin](/help/pin-a-stream) or star important streams,
[change the colors](/help/change-the-color-of-a-stream) of streams, and enable desktop
notifications or muting for streams in order to create a better Zulip
environment.

If enabled by the realm administrators, users can
[create](/help/create-a-stream) streams and [invite](/help/add-or-invite-someone-to-a-stream)
other users to a stream.

Only realm administrators can make edits to a stream, such as
[renaming](/help/rename-a-stream), [deleting](/help/delete-a-stream), changing the
description of a stream, [removing users](/help/remove-someone-from-a-stream) from a
stream, or changing the accessibility of a stream.

## About topics
In each stream, messages are sorted by topics. Topics are
specific, fine-grained subjects that fit with the overall subject of the
stream that they're sent to. Topics ensure sequential messages
about the same thing are threaded together, allowing for better consumption
by users.

The best stream topics are short and specific. For example, for a bug tracker
integration, a good topic would be the bug number; for an integration like
Nagios, the service would serve as a good topic.

Users can easily [change the topics](/help/change-the-topic-of-a-message) of the messages
that they sent if they sent the message to the wrong topic or if some
messages in a topic have gone off-topic.