A hinge is something that connects two objects and lets them rotate. The most common examples are the hinges that connect doors to walls or door frames. To open a door on hinges, one pushes the side far from the hinges and the door rotates around the side with hinges.
Hinges can be very large or very small. Small hinges are used for jewelery boxes and other small things with lids. Very large hinges have been used at the bottom of buildings, to let a building sit on loose soil or mud without breaking.