A Weaver rail mount (Picatinny type) is a system to connect peripheral accessories to rifles, shotguns, pistols, archery bows, etc. The Picatinny rail is a bracket used on some firearms in order to provide a standardized mounting for sniper scopes and other accessories. ...
The Picatinnyrail is a bracket used on some firearms in order to provide a standardized mounting platform for scopes and other accessories such as tactical lights and laser sighting modules.
The rail is typically placed directly on the weapon's receiver, in the position normally occupied by the rear sights.
Shaped in cross-section roughly like a wide T, scopes are mounted on the rail either by sliding them on from one end or the other, or by means of a "rail-grabber" which is clamped to the rail by means of bolts, thumbscrews or levers.