Column.—A formation in which the elements of a command are placed one behind the other. The elements here referred to may be troopers, twos, fours, sections, platoons, or larger units. When used in these regulations as a word of command, without qualifying words indicating the kind of column (as of twos, of platoons, etc.), column signifies a column of fours. In all other cases the word is to be understood in its general sense unless the context indicates the contrary.
Deployment.—An evolution in which the command extends its front, as in forming line from column or in passing from close order to extended order.
Depth.—The space from front to rear of any formation, including the front and rear elements.
Directing leader.—The leader of a subordinate unit who temporarily conducts the march when the commander is not leading in person. A trooper in the rank of a platoon or smaller unit who similarly conducts the march is termed a directing guide.
Direction of march.—The direction in which the base of the command in question, whether actually in march or halted, is facing at the instant considered.
Disposition.—The distribution of the elements of a command, and the formations and duties assigned to each for the accomplishment of a common purpose.
Distance.—The space between men or bodies of troops measured in the direction of depth. Distance is measured—mounted, from the croup of the horse in front to the head of the horse in rear; dismounted, from the back of the trooper in front to the breast of the trooper in rear.
Dress.—The act of taking a correct alignment.
Drill.—The exercises and evolutions, taught on the drill ground and executed in accordance with definitely prescribed methods.
Echelon.—A body of troops is in echelon with reference to another when it is more advanced or less advanced and unmasks or uncovers the other body, wholly or in part; units thus placed are called echelons.