Entertaiment is anything that diverts or amuses people during their leisure time. Examples of this are playing a sport as a hobby, or solving the daily crossword puzzle. It can also refer to a specific activity, such as attending a theatre show.
Brain entrainment works by using sound or light to synchronise brainwaves to a particular frequency, like gamma 40 hz. Over several sessions, the new firing pattern becomes ingrained and no longer needs to be stimulated.
The strength of the zeitgeber is critical for entrainment to be effective. The length of time it takes for an organism to readjust after a phase shift is proportional to the strength of the zeitgeber. Cockroaches take 4 days, rats 8 and humans 11 days.