c-string
A strapless thong shaped like a C, playing on the word g-string. The c-string uses a flexible frame to hold itself to the body without straps to avoid tanlines.
Generally, this would preclude a cameltoe but rules of artistic license apply. If a potential c-string doesn't continue all the way up into a back thong "strap" or if it clings too tightly to the body, it might be a maebari instead.
See also
This tag implicates strapless_bottom (learn more).