Mentions

If you want to get a specific user’s attention, the best way to do that is usually with a “mention”, a concept popularised by social media sites like Twitter.

To mention a user in Discourse, you start by typing the @ character immediately followed by the first letters of that someone’s username. If you’re posting in an existing topic, Discourse will intelligently push active topic participants to the top of the auto-completion list.

http://erlend-sh.github.io/images/discourse-mentions.mp4

Typing a part of a user’s full name will also work.

Further Reading

• Inviting Existing Users

• Discussion: Group Mentions

Source: https://meta.discourse.org/t/what-are-mentions/32788