rash Breaking out (eruption) of the skin. A rash can be caused by an underlying medical condition, hormonal cycles, allergies, or contact with irritating substances. Treatment depends on the underlying cause of the rash. Medically, a rash is referred to as an exanthem.
rapid eye movement sleep See REM sleep.
range of motion The full movement potential of a joint, usually its range of flexion and extension. For example, a knee might lack 10 degrees of full extension due to an injury.
range In medicine and statistics, the difference between the lowest and highest numeric values. For example, if five premature infants are born, weighing 2, 3, 4, 5, and 6 pounds, respectively, the range of their birth weights is 2 to 6 pounds.
random sample A test group that is selected solely by chance.
random mating Totally haphazard mating, with no regard to the genetic makeup (genotype) of the mate, so that any sperm has an equal chance of fertilizing any egg. Random mating rarely, if ever, occurs, but the concept is important in population genetics. Also known as panmixus.
random Determined solely by chance.
ramus of the mandible One of the two prominent, projecting back parts of the horseshoe-shaped lower jaw bone.
ramus In anatomy, a branch, such as a branch of a blood vessel or nerve. For example, the ramus acetabularis arteriae circumflexae femoris medialis is the branch of an artery that goes to the socket of the hip joint. The plural of ramus is rami.
Ramsey Hunt syndrome A herpesvirus (specifically, by the varizella-zoster virus or VZV) infection of the geniculate nerve ganglion, which causes paralysis of the facial muscles on the same side of the face as the infection. It is usually associated with an unusual rash (composed of vesicles, or tiny fluid-filled bumps, in the skin) in or…
rale An abnormal lung sound that can be heard through a stethoscope. Rales may be sibilant (whistling), dry (crackling), or wet (sloshy), depending on the amount and density of fluid refluxing back and forth in the air passages.
RAI Radioactive iodine.