The term 'Army Groups' refers to the largest military formations in the Army, consisting of two or more field armies and other supporting units. These groups are typically commanded by a general or lieutenant general and are responsible for coordinating operations on a large scale. The term 'Units' is used to refer to the smaller sub-units within an Army Group, such as battalions, regiments, and brigades. These units are typically commanded by a colonel or major and are responsible for carrying out specific tasks within the larger group.