Trench

A trench is a long, narrow ditch.

Trench warfare has often been used in defense. Entrenched soldiers can be somewhat safe from enemy fire. Trench warfare made World War I longer than expected. The trench coat got its name from there.

Several kinds of trench exist:

Utility trench has pipes, wires, or other infrastructure
Road trench carries vehicles
Military trench provides shelter for soldiers shooting at each other
Oceanic trench: For example, the Mariana Trench
Rift valley
Archaeological trench dug by archaeologists