A sniper rifle is any rifle that has been modified to increase accuracy at extreme ranges, as part of a process referred to as "accuratization." The operator of such a weapon is known as a "sniper" after the snipe, a small, fast bird which is difficult to shoot when hunting.
There is no precise definition of a sniper rifle. However, a modern sniper rifle will almost certainly have a telescopic sight. It may also include other modifications such as a heavier, longer stock to increase accuracy, a special "cheek mount" for the operator to rest his cheek on when firing from a prone position, and a mount such as a bipod or monopod. Sniper rifles are often traditional bolt action rifles. However, semiautomatic rifles may also be used.