Active service

What does Active service mean in American Law?

The definition of Active service in the law of the United States, as defined by the lexicographer Arthur Leff in his legal dictionary is:

A person on “active service” in the Armed Forces is not necessarily engaged in fighting or even preparing for it. He is merely performing some duties, as distinguished from being in civilian life waiting to be called or recalled to active service. One who is in the “active reserves” is in civilian life, but nonetheless ordinarily engages in some regular training regimen, e.g., one night per week and two weeks during the summer.