A one piece bathing suit consisting of only the top piece and nothing on the bottom. Can also be wearing a bra and no panties. Can be used in any situation where a top is on and nothing is covering below the waist, bottomless.
"Hey check out that chick over there in the waves. She's bangin!"
"Yea and she's rockin a Hermsen One-Piece so we got a looksie at that bare ass!"
Hey did you see that Harold and Kumar movie with the bottomless party where every girl was rockin a Hermsen One-Piece?