The cheap ceiling texture commonly used in the 70s and 80s. Builders would spray 'popcorn' on the ceilings of homes and justify it to sellers by feeding them a line of bull about better sound insulation or better appearance. The real reason for the 'popcorn' it turns out is because its cheap and if a builder does have to pay some guy to texture and paint every ceiling, it can save them some serious money. The 'popcorn' unfortunately does nothing for sound insulation (though there might still be those today who claim it does) and it's pretty damn ugly, especially as it collects dirt over time.
Omg! That sauce just got all up in the popcorn ceiling! That shit is never coming off!