Reputation is a (very) rough measurement of how much the Area 51 community trusts you. Reputation is never given, it is earned by convincing other users that you know what you're talking about.
As you earn reputation from your peers, you earn the community's trust – and will be granted additional privileges on Area 51.
The complete list of privileges is listed on the right, in ascending order. The most basic privileges are at the bottom; the most advanced at the top.
Click on any privilege to learn more about it.