Bowls or lawn bowls is a sport in which the objective is to roll biased balls so that they stop close to a smaller ball called a "jack" or "kitty". It is played on a bowling green which may be flat (for "flat-green bowls") or convex or uneven (for "crown green bowls"). It is normally played outdoors (although there are many indoor venues) and the outdoor surface is either natural grass, artificial turf, or cotula (in New Zealand).