O'CLOCK Shadow is a term used to describe the length of a person's shadow at a certain time of day. It is usually used to refer to the length of a person's shadow at noon, when the sun is at its highest point in the sky. The term is derived from the phrase 'at the stroke of twelve o'CLOCK, ' which is used to indicate the exact moment when the sun is at its highest point. The term is also used to describe the length of a person's shadow at any other time of day.