a pattern of EEG waves,

Spindle-shaped bursts of 11.5-15 Hz waves lasting 0.5-1.5 seconds. Generally diffuse, but of highest voltage over the central regions of the head. The amplitude is generally less than 50 uV in the adult. One of the identifying EEG features of NREM stage 2 sleep; may persist into NREM stages 3 and 4; generally not seen in REM sleep.

An episodically appearing, spindle-shaped aggregate of 12-14 Hz waves with a duration of 0.5-1.5 seconds, one of the identifying EEG phenomena of NREM stage 2 sleep; may persist into NREM stages 3/4: not seen in REMS.