Here's how it goes..

Newcomer: less than 10 posts

Resident: someone who has more than 10 posts

Citizen: someone who has more than 100 posts

Pillar: someone with more than 1,000 posts


You are able to change it to anything you want once you become a citizen.

To do this, you go to your User CP.
Then to edit profile.
Then you scroll down to "Custom User Text"
Type in what you want in the area under "New Title"
The click Submit Modifications to save it.