You’ll find four types of channels in Mattermost: public channels, private channels, direct messages, and group messages.
Public channels are open to everyone on a team and are identified with a icon. New team members are automatically added to two public channels when they sign up: Town Square and Off-Topic. See the Join and Leave Channels documentation for details on discovering and joining other channels.
Private channels are for sensitive topics and are only visible to selected team members. Private channels are identified with a icon. In Team Edition, any member of a private channel can add or remove other members from private channels, but in other Mattermost versions these permissions can be restricted to the Channel Admins and System Admins.
Channel members can choose to leave private channels at any time.
Direct messages are channels for conversations between two people. You can also start a direct message with people on other teams when enabled by the System Admin. Only members of the conversation can see direct messages.
Group messages are channels for conversations among three or more people and up to seven people. You can also start a group message with people on other teams when enabled by the System Admin. Only members of the conversation can see group messages.
Create a private channel to communicate with more than seven people.