Messages and threads
Threads are a key part of the messaging experience in Mattermost. They’re used to organize conversations and enable users to discuss topics without adding noise to channels or direct messages.
Collapsed Reply Threads offers an enhanced experience for users communicating in threads and replying to messages that includes a unified threads inbox to read all conversations in one view. Threads improve the ability to process channel content, find, follow, and resume conversations more easily, and keep threaded conversations focused.
More information can be found on the official Mattermost documentation