Copied it from reddit, I hope it's enough:
Spear: long shaft of wood with a metal tip. Can be used for stabbing or throwing.
Javelin: short shaft of wood with a sharpened end. Used for throwing.
Lance: A long and thicker pointy piece of wood designed to be carried by a horseman. Far too inconvenient for a single man to carry.
Pike: very very long staff with a metal dagger-like item strapped to the top. Used for foot soldiers to stab at horsemen from a safe distance.