Well a Springlock is, put simply, a device that can lock in place using a special spring and lock mechanism. These devices actually exist in real life. Springlocks can be used to firmly hold various things back in a certain position. This is the use that is relevant to FNAF.

What are spring lock suits?

A Springlock suit is a special animatronic that can be used as both an animatronic and suit. In order to turn the animatronic into "suit mode", you will require a special crank which pushes the endoskeleton and other robotic bits into the sides of the suit, making just enough space to fit a person inside.

What does spring locks do in FNaF world?

Springlocks is an attack in FNaF World. It is fittingly used by Springtrap and Spring Bonnie. It deals a minimum of 250 damage and a maximum of 1000+ damage, and it will hurt enemies that are nearby the one that was hurt. Springlocks is the most powerful Red attack in the game, along with Freddles, in second place.