There are three types of channels in Zulip:

* [Private channels](/help/channel-permissions#private-channels)
  (indicated by <i class="zulip-icon zulip-icon-lock"></i>), where
  joining and viewing messages requires being invited. You can choose
  whether new subscribers can see messages sent before they were
  subscribed.

* [Public channels](/help/channel-permissions#public-channels)
  (indicated by <i class="zulip-icon zulip-icon-hashtag"></i>), which
  are open to everyone in your organization other than guests.

* [Web-public channels](/help/channel-permissions#web-public-channels)
  (indicated by <i class="zulip-icon zulip-icon-globe"></i>), where
  anyone on the Internet can see messages without creating an account.