Bikini tops that are worn in place of a bra, normally covered by a tank top, wife beater, or shaggy old vintage beach tee. Bathing Bras are worn when one has the intention of going to the beach, pool, or fitting into a socal stereotype during the summer months of the year. Used as a support system, even though we all know bikini tops don't provide that much support...
Michael: Why are you always wearing your bikini top under your tanks?
Erica: This isn't a bikini top, this is a bathing bra dude.