Derived from the military practice of closing the spacing between lines (ranks) of troops, as they are deployed across a battlefield, thereby decreasing the depth of the formation as it faces the enemy side. This practice allowed for the second rank to fire their weapons without movement, sidestepping, and firing alongside, and slightly to the rear of the first rank. The opposite would be to open ranks. The columnar equivalent when not deployed for battle would be to close or extend the column.
- (idiomatic) To regroup forces, especially when this involves overlooking differences in order to face a challenge or adverse situation. Often implies making a show of unity, especially to the public.