What name is given to a hole in the ground that soldiers use as a shelter against enemy fire?

A foxhole is one type of defensive strategic position. It is a "small pit used for cover, usually for one or two men, and so constructed that the occupants can effectively fire from it."

During the fighting in North Africa (1942-43) Specifically in Tobruk - Libya, U.S. forces employed the shell scrape. This was a very shallow excavation allowing one man to lie horizontally while shielding his body from nearby shell bursts and small arms fire. The slit trench soon proved inadequate in this role, as the few inches of dirt above the soldier's body could often be penetrated by bullets or shell fragments. It also exposed the user to assault by enemy tanks, which could crush the man inside a shallow slit trench by driving into it, then making a simple half-turn.

After the Battle of Kasserine Pass (early 1943), U.S. troops increasingly adopted the modern foxhole, a vertical, bottle-shaped hole that allowed a soldier to stand and fight with head and shoulders exposed. The foxhole widened near the bottom to allow a soldier to crouch down while under intense artillery fire or tank attack. Foxholes could be enlarged to two-soldier fighting positions, as well as excavated with firing steps for crew-served weapons or sumps for water drainage or live enemy grenade disposal.