Regular bomb: dumb and unguided, falls downwards, needs to be dropped on top of an enemy that's probably trying to prevent you from getting into position to do so.
Glide bomb: cool wings and rudders and stuff, glides horizontal and pretends to be a cruise missile, can be dropped from safe a distance away where nobody can shoot back.
Dumb bomb is gonna fall basically where you drop it. Smart bomb is gonna fall very accurately where you drop and steer it. Glide bomb gets dropped and then glides to somewhere else where you wanna drop it.