The space extremely close to the ground, lower than what is typically considered low altitude; often used in the context of flying at a minimum altitude.

The sport of jumping from a fixed object, such as a building, antenna, span, or earth, using a parachute to break the fall

(metaphorical) to just scrape through with a narrow pass, as in an exam or a test; literally, to fly past at low altitude

flying at an extremely low altitude; hedgehopping