Kind of like a g-string only more revealing. Piece of women's underwear that consists of a C shaped (hence the name) semi-flexible band that is very narrow at one end and slightly wider at the other end (somewhat like an unbalance hair band). The C-String essentially clamps onto the woman's body with the wide end covering the pubic region (just barely and only if she's is very well groomed) and the narrow end extending up the crack of the ass. The C-string completely eliminates panty lines and if used sunbathing removes 99% of tan lines. It also eliminates a woman's confidence that her underwear will actually stay on all day long.
Carrie wore her C-string with her dress that laced up the side and she was quite a sensation, since she appeared to be going commando. She was an even bigger sensation when she dropped the C-string on the dance floor and had to explain to her date what it was.