1.adj. pertaining to the two lips. 2.adj. denoting a speech sound made with both lips, which stop or modify the airstream, for example, [b], [p], [m], or [w]. 3.n. a bilabial speech sound. See labial.
deep sleep that is characterized by increasing percentages of particular types of delta waves on the electroencephalogram, corresponding to Stages 3 and 4 of NREM sleep. See also sleep stages.