Audio-visual entrainment, a subset of brainwave entrainment, uses flashes of lights and pulses of tones to guide the brain into various states of brainwave activity. AVE devices are often termed light and sound machines or mind machines. Altering brainwave activity is believed to aid in the treatment of psychological and physiological disorders.
I have my own AVE device and use it for meditation mostly. It was introduced to me in therapy as an adjunct to Neurlofeedback QEEG therapy.