Binaural beats are frequencies which are generated through subtracting one frequency from another and it's an acoustic phenomenon called "beating". This allows you to generate frequencies which can't be produced by regular loudspeakers or headphones. However, if you listen to one frequency with one ear and another frequency with your other ear, your brain will interpret it as hearing a frequency equal to the difference between them (beating) as long as the difference is smaller than about 50 Hz. The reason is that frequencies lower than about 50 Hz are rather felt than heard, so differences bigger than 50 Hz would be heard as an interval instead of actual beating.

For example: f1 = 100 Hz and f2 = 110 Hz.
The resulting binaural beat will be:
f2 - f1 = 110 Hz - 100 Hz = 10 Hz.
Binaural beats are used in neuroscience to stimulate different brain waves within the range 1 Hz - 40 Hz. More info on this link.
Hint: you can use decimal values for frequencies, i.e. 426.7