What are ranks?

Some abilities in Brink can only be purchased if your "rank" is high enough. All I know is that at some point, for some reason, I got to rank 2.

Are ranks level milestones? How can I see my progress towards the next rank?

(I've tried to register for my online stats, but they'll only be refreshed in 15 hours for some reason. I also can't see anything about rank there.)

Yes. The requirements are as follows:

• Rank 1: 0 XP (Level 0 through 4), the Rank you start as.
• Rank 2: 15,250 XP (Level 5 through 9)
• Rank 3: 60,750 XP (Level 10 through 14)
• Rank 4: 148,000 XP (Level 15 through 19)
• Rank 5: 300,000 XP (Level 20)