Ice skates are boots with blades attached to the bottom, used in ice skating to propel oneself across ice surfaces.
A clap skate (or clapper skate) is a type of skate where the shoe is connected to the blade using a hinge.
The steel ice skate was invented in 1867 by John Forbes, foreman at the Starr Manufacturing Company, Dartmouth, NS. It was a clip-on design. Their Acme brand became famous worldwide.
Modern ice skate blades are not shaped like knives. The bottom of the blade has a crescent-shaped hollow, creating two parallel sharp edges on each skate (recently, parabolic blades have been developed as well). The skater uses these edges in different combinations in order to maneuver. When ice skates are sharpened the blade is ground against a template that restores the hollow. Sometimes, however, there is a back brake, which is a point that stops you from moving any further.
Modern amateur ice hockey skates
Modern recreational skates