A QD socket is a Quick Disconnection system that was initially designed for the firearms industry and then later adopted by the photography industry. The QD system is a 2-part system that featured a QD socket on the camera plate, and a QD Swivel that mates with the socket once the button is depressed. The system is extremely strong and robust, thus able to hold even the largest cameras and super-telephoto lenses with ease.
Photography industry companies such as Really Right Stuff, Kirk Photo, Hejnar Photo and Blackrapid all make products that are designed around the QD system. All QD straps from the firearms industry are also usable on camera gear that features a QD socket.