Considered to be NREM light sleep, follows stage 1 in both children and adults with brain wave forms occurring about 12-14 cycles per second of low voltage but mixed frequencies, and marked by K-complexes and sleep spindles; arousal threshold is a bit higher than what is needed to awaken a person from stage 1 sleep.
See Behavioral state, Behavioral state concept, EEG stage 3 sleep, EEG stage 4 sleep, Electroencephalogram (EEG), NREM sleep, Sleep architecture