Veteran levels are what you earn after level 50, when the normal XP leveling process stops. If you notice your XP bubbles once at lvl 50, they are still filling as you do content that earns XP. You still ding-rez and get the usual inspiration bonus, and every set number of times you totally fill all ten bubbles, you'll earn Emp Merits. I believe it's every three or so veteran levels for a bit, and then it happens less often. It's a way for you to earn your Incarnate stuff faster and not have to run Trials all the time, as some folks have a hard time getting to do them. If I have any info wrong, feel free to correct me.