An anti-tank trench is a very deep and wide hole that is meant to stop big, heavy vehicles called tanks from moving forward. Imagine digging a hole that is so big you could fit a car inside it, and then making it even deeper so that the tank can't drive over it. This is what an anti-tank trench looks like.
When an army is fighting a war, they may use tanks to move around and attack their enemies. But the other army might try to stop the tanks in their tracks by digging these huge trenches in the ground.
The trench is usually filled with dirt or other materials that make it very hard for a tank to get through. The goal is to force the tanks to go around the trench, which slows them down and makes them more vulnerable to attack.
Anti-tank trenches were used in many wars throughout history, including World War I and II. They can be very effective in stopping tanks, but they are also difficult and time-consuming to dig.