A drawbridge is a bridge where it stops enemies from getting into the castle. It can be raised or lowered so the enemies have to walk through the water and break the door down. A drawbridge is made out of wood and has a metal plate at the back to reign force it so it doesn't burn all the way down. The drawbridge is usually for a castle with a mote.
We got this drawbridge picture from http://www.castles-of-britain.com/castlesp.htm