rem

The amount of ionizing radiation required to produce the same biological effect as one rad of high-penetration x-rays.

A unit for measuring absorbed doses of radiation, equivalent to one roentgen of x-rays or gamma rays.

Acronym rapid eye movement, a sleep state.

A dose of absorbed radiation equivalent to one roentgen of X-rays or gamma rays.

A remark; a programming language statement used for documentation (in BASIC for example); also used in DOS batch files.