A crampon is a traction device that is attached to footwear to improve mobility on snow and ice during ice climbing. Not only are crampons used during ice climbing, but they are also used for secure travel on snow and ice, such as crossing glaciers, snowfields and icefields, ascending snow slopes, and scaling ice-covered rock. There are three main attachment systems for footwear: step-in, hybrid, and strap bindings. The first two require boots with welts, as a tension lever attaches the crampon to the heel. The last type (strap bindings) are more versatile and can adapt to virtually any boot or shoe, but often do not fit as precisely as the other two types. (source)