To flank means to be positioned at the side of something or someone. In a battle, soldiers might flank the enemy by moving around to attack from the side rather than head-on. A bodyguard might flank an important person, standing beside them for protection. Two tall buildings might flank a city plaza, standing on either side of the open space.

As a noun, a flank is the side of something. A horse's flank is the area between its ribs and hip. A mountain's flank is its slope or side. In football, players run around the flank of the defensive line rather than charging straight through the middle.

You might also encounter flank in cooking: flank steak is a cut of beef from the side of a cow, known for being flavorful but needing careful preparation.

Whether describing position, movement, or strategy, flank always involves the side rather than the front or back.