What does "marching" mean?

Marching: ,fr. March, v. Marching money (Mil.), the additional pay of officer or soldier when his regiment is marching. -- In marching order (Mil.), equipped for a march. -- Marching regiment. (Mil.) (a) A regiment in active service. (b) In England, a regiment liable to be ordered into other quarters, at home or abroad; a regiment of the line.