A device that attaches to a
plastic boot, or sometimes a leather boot will a full
steel shank, which helps you gain a
purchase in
snow or
ice, and in effect, gain
traction.
Crampons come fully rigid, which is used mainly for vertical ice and waterfall ice. They also have models which are semi rigid, with hinges. This allows for the crampon to bend with your foot as you walk. These are used mainly for glacier travel and ice which is less than fifty degrees.
Crampons can bind to your feet with straps, or bails, or a combination of which. Crampons which are bailed are usually called step-in crampons and these are used mainly on vertical ice. The strap on crampons are a little cheaper, less technical, and are used on the less demanding glaciers, or sometimes in combination with snowshoes which allow crampons.
Crampons are often sold and classifed by the number of points, and how the points are arranged. The classic crampon is a 12 point crampon with four points on the heel six points around the ball and sides of the feet and two forward, for front pointing. Sometimes they are sold in a 10 point variety.
The more technical crampons have changable front point configurations. Recently a mono point has been a newly accepted way to climb vertical ice. But, it's really personal preference.
The big boys in the crampon market are Grivel, Charlet Moser, Black Diamond, and Camp 12. They will usually cost you $130 for a low level crampon with straps, and upwards of $180 for a technical ice crampon.
Crampons are not to be confused with tampons. My ex-girlfriend finds it entirely amusing to tell me I don't need crampons because I don't have a period every time I talk about them.