A selfbolting door is called as such because of its special hinge

Hinge

A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components...

s that permit the panel leaf to move laterally so that the door itself becomes a giant bolt for better security result. The selfbolting door principle can be used both for hinged doors as for rotating doors, as well as up-and-over doors (in the latter case, the bolts are then placed at top and bottom rather than at the sides).