From publisher blurb:
While the cavalier or paladin tends to ride their opponents down with the force of their weight and their mount, the hussar rides a lighter beast and relies on speed and agility. She relies on her skill as a rider and trusts in her mount rather than heavy armor to stay safe and makes quick, darting hit and run attacks with a sword, polearm, or even ranged weapons.
The Hussar's role is to harry at the edge of battle, picking off those who stray too far from line or formation. They fight in an active style somewhat similar to the rogue, but may also be sought out for their skills as riders and sometimes even as trainers.