Aft is a nautical term used to describe the rear section or back end of a boat or ship. It is the exact opposite of the bow or forward of a ship, which is the term for the front end of a vessel. The underside of the aft is where you will find the propellers, engine compartments, and steering rudder. The term "aft" is derived from an Old English word spelled "aeftan," which roughly translates to "behind" or "in the back of".