A trench is a type of excavation or depression in the ground. Trenches are generally defined by being deeper than they are wide (as opposed to a wider gully or ditch), and by being narrow compared to
their length (as opposed to a simple hole). Trenches are a natural feature in many landscapes. Some are created by rivers in flow (which may have long since fallen dry), others are features created by geological movement, such as oceanic trenches. The latter form is relatively deep, linear and narrow, and is formed by plate subduction. [Wikipedia]