A representation of someone's skill at horseback (or anything-back) riding, and the ability to perform difficult feats of riding without being thrown and paralyzed from the neck down. Particularly useful for say, jousting knights.
0: You can climb on top of a horse sure, and leisurely let them go where they please if they are well trained, but you can't escape their judging, horse-y eyes. They know.
1: You have fair odds of galloping around without acquiring a crippling spinal injury.
2: Most mounted knights are at least this proficient, and quite capable of charging across a field and trying to avoid being impaled by pikemen.
3: Your horse is extremely appreciative of your ability to avoid holes or not making ill advised jumps.
4: Someone capable of racing through terrible conditions without getting themselves or their horse killed.
5: There's gotta be someone responsible for the persistent rumors of bear cavalry in the Northlands.
6. Dragons argued for who gets to have you as the rider.