A Lance Knight is a horse-mounted class of units (Lance Knight Eldritch are mountless, but hold the same mobile capabilities). As the name suggests, Lance Knights wield Lances, and can equip a Lance or Shield. Being a mounted unit, Lance Knights can move a farther distance than most base classes.
Aside from that, Lance Knights typically lean towards fairly balanced stats, excelling in Strength and Guard, and badly lacking only in Magic and Spirit. This in addition to their Movement stat of 6 makes a Lance Knight a pretty dependable support unit, being able to block off enemies to protect the back when necessary, or pick up the slack of any of the players' less powerful units.