It's right in the description

That (urban-legend-coded, totally-trippy-if-you're-fifteen-years-old) app introduced me to "Binaural Beats" - where you play two different tones in each of a person's ears, and the brain scrambles the different frequencies into a single frequency. As I understand it, this is meant to induce specific brainwaves in the listener, which replicate states like "deep focus" or "half-asleep" or "meditating". I've not decided personally if this is real science, or new-age pseudoscientific nonsense. It's probably somewhere between the two.