A spanner is a tool that is used for tightening and loosening nuts, bolts, and other fixtures. It typically has two sets of points at each end for turning a nut or bolt in either direction. The most common type of spanner is the adjustable spanner, which allows for greater grip and flexibility. Other types of spanner include ring, ratchet, and box spanners. These are used for specific tasks and offer different levels of torque.