What is Cap?

Legal Definition
A cap is a form of headgear. Caps have crowns that fit very close to the head and have no brim or only a visor. They are typically designed for warmth and, when including a visor, blocking sunlight from the eyes. They come in many shapes and sizes.
-- Wikipedia
Legal Definition
An OVERTHECOUNTER INTEREST RATE OPTION contract that provides the buyer with a payoff when an underlying interest rate reference exceeds a predefined STRIKE PRICE. See also CAPTION, FLOOR, FLOORTION.