That's a term used to describe the ratio between the fighting people getting shot at and the people in the rear doing support. At the peak of the Vietnam War, there were over 500,000 American servicemen in-country but at no time did the number of actual combat troops exceed 100,000.

No combat force can long exist without logistics support, medical services, air support, and a host of other jobs. Most of those jobs are performed by hard working and dedicated people in the rear areas. Most combat arms personnel recognize this fact and respect the people who do them.

The term "REMF", while sometimes used to describe the good people in the rear, was more often applied to a different breed of rear area personnel. These REMFs were people who used connections to keep themselves safe, did little or nothing to contribute to the mission, and even enriched themselves at others expense.

I went into the Army right out of high school in 1975. I served with a lot of Vietnam vets and many of them had some harsh words for the REMFs. They resented how quite a few REMFs kept the best gear for themselves and had a pretty cushy time of things while the combat troops were getting shot at. Quite a few of the REMFs became notorious for giving each other medals to inflate their military records while doing little or nothing to actually fight a war.

Not all Vietnam vets are created equal. There were a lot of guys who spent their nights in the jungle or the rice paddies, but there were a lot more who had it pretty good. I went to electronics school with a former Army pilot who described Nam as "the best kept secret in the world." He voluntarily served 2 tours over there and wanted to stay longer because he had it so good. He was one of those REMFs who played the system and made a lot of money while seldom exposing himself to danger. Combat troops despised people like him.