A crossbow is a weapon consisting of a bow mounted on a stock that shoots projectiles, often called bolts or quarrels. It works in much the same fashion as a regular bow, but replaces manual pulling of the bowstring with the use of a mechanical device, such as a lever or a crank, to draw back the string, allowing for more powerful shots in exchange for being quite slow to load and shoot in comparison to a regular bow. Crossbows in general are easier to use than regular bows, which require more strength to pull back the bowstring.
This tag implicates bow_(weapon) (learn more).