a unit of frequency, commonly used to measure rotational speed, in particular in the case of rotation around a fixed axis. It represents the number of full rotations something makes in one minute. 
Gramophone (phonograph) records typically rotate steadily at 16, 33, 45 or 78 rpm. Audio CD rotation rates vary from about 500 rpm when reading the innermost data track, to 180 rpm when reading tracks near the outer edge.