In engineering, a boss is a protruding feature on a work piece. A common use for a boss is to locate one object within a pocket or hole of another object. For instance, some motors use a precisely machined boss on the front face to locate it on the mating part. Like a process on a bone, bosses on castings can provide attachment points or bearing surfaces. A boss can also be a brass eyelet on a sail. It is a generic term to describe an item designed to facilitate the use with, within, on or around another item whereby one cannot operate properly without the other.