“An excavation is any man-made cut, cavity, trench, or depression in an earth surface formed by earth removal.
Trench means a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench (measured at the bottom) is not greater than 15 feet.”
Reference: OSHA Fact Sheet, Trenching and Excavation Safety.