G thang - AKA butt floss.........

Definition : A thong, tanga or g-string is a narrow piece of cloth or leather that passes between the legs and is attached to a band around the hips, worn as a bikini bottom or as underwear. It is sometimes disparagingly called butt floss, referring to its tendency to slide between the buttocks like dental floss between the teeth. – wikipedia

What is a Whale Tail?: (NSFW) a girls G-string or Thong that becomes exposed as she walks, bends over or squats.....
Some floss found on the net: