Orders and commands

"There is a sharp distinction between an order and a command, although both are used somewhat indiscriminately in referring to either. An order leaves the manner of execution in general up to the recipient of the order. An order does not always specify just when it shall be executed, but frequently fixes a certain time by which it must be executed. A command leaves nothing to the discretion of the recipient. It usually is peremptory, arbitrary, and implies execution at the time of its receipt unless otherwise specified."

Manual of Orders and Commands
1945