Picatinny rail
The only significant difference between the Picatinny rail and the similar Weaver rail are the size and shapes of the slots, where the Picatinny rail has square-bottomed slots while Weaver rails have rounded slots. This means that an accessory designed for a Weaver rail will fit onto a Picatinny rail whereas the opposite might not be possible (unless the slots in the Weaver rail are modified to have square bottoms.)