The phrase "sound sleepers" refers to people who sleep deeply and are not easily disturbed by noise or movement while they are sleeping. Full definition
If you have a really sound sleeper, you might even consider doing a diaper change before you go to bed. (babygaga.com)
I can barely remember how it felt to be that sound sleeper anymore! (wellnessmama.com)
Contributors include Rebecca Nazzal of Dream Big Sleep Consulting, Jennifer Schindele of Gift of Sleep Consulting, Ronee Welch of Sleeptastic Solutions, Visa Shanmugan of Sound Sleepers, Violet Ginnone of Sleep Baby Sleep, Tamiko Kelly of Sleep Well. (care.com)