Public Groups and Channels.
All groups and channels are private by default, but you can make them public and open for any user to join or subscribe.

Public groups and channels have unique t.me links, appear in Global Search results, can reach an unlimited audience and host massive communities for any interest.

You must be the chat owner to change the group or channel type. On Android tap the Chat Header > > Group/Channel Type. On iOS tap the Chat Header > Edit > Group/Channel Type.