A crossbow is a special type of bow. The flexible limb (lath or bow) is attached to a central stock. The lath is also referred to as the prod in the US. The string is drawn back by manual or mechanical means and is held in position by a catch or lever. The weapon can then be loaded with a crossbow bolt or quarrel, which is basically a stick or metal rod, perhaps with feathers, parchment or leather to stabilise the quarrel in flight. The heads were frequently much larger than arrowheads and consisted primarily of bodkins style points. To fire, the user just aims the stock in the direction of the target, and releases the string.
It is a very powerful weapon but its lack of accuracy makes it really only effective over a short distance.
A larger weapon that works like a crossbow is a ballista.
Crossbows in the SCA
Archers may also find that they are required by state, territory, province or federal laws to hold a license for their crossbow. This is particularly important to check when going to any event outside your normal group, e.g. interstate or international.