Binaural Beats are an audio stimuli that use sub-audible frequencies to synchronize the left and right hemispheres of the brain to a desired brainwave pattern and effect. 

Headphones are necessary when listening to binaural beats to gain the full benefit. Binaural beats work by playing two separate audible frequencies into each ear. The difference of those frequencies is the binaural beat frequency.

As an example, to replicate a sub-audible 5Hz theta frequency you could play 200Hz in the right ear and 205Hz in the left ear. The difference in frequencies creates a “wub” or “beat” sound that occurs in the listeners brain. This works similar to a tuning fork to help entrain the brain to the desired frequency pattern. Theta range audios in particular are known to assist listeners in reaching deeper states of meditation.