Formations

In SCA heavy weapons combat, the most common formation called the shield wall. This can be as simple as having everyone with a shield make a line, shoulder to shoulder. Everyone else gets behind them. Some commanders/units will add order to the back field.

Reserve unit

A group of fighters held behind the shield wall in case a problem or opportunity develops.

Flanking unit

A group of fighters whose assigned task is the execute a Flank Right/Left independent of the main group's motion.

Columns of 2/3/4

The unit forms into 2/3/4 lines for marching with no expectation of attack (because the battle hasn't started yet and you're all trying to get through a small gate.)