Takedown Lever
A lever or pin used to release a pistol's slide for disassembly.
Also: takedown pin
The takedown lever is the disassembly control — typically rotated or pulled out to free the slide from the frame for cleaning. Different platforms use very different mechanisms: the 1911 uses a slide stop and barrel bushing; Glocks use a small lever pulled down with the trigger pressed (yes, on an unloaded gun); the AR-15 uses two captive push pins.