Member titles in PMs?

Sooo, sorry this is a dumb question, but I've noticed that when I'm PM'ing people, the people I PM have these little titles beneath their username and avatar. Like senior writer, novice, novelist, forum master, etc. What are those? And how do they get them?

Those titles are based on your post count. The more posts you have, the more grand your title!

I forget the exact post counts for each title, but they don't really feature outside of the PMs, so most people just ignore them.

Yeah those titles used to be more prominent on the site, featured near the avatars on posts. You could even pick your own title after 250 posts. But it's been a long time since they were used. I guess they still show up on PMs, but that's it.