whale tail – the appearance of the top rear strap of a woman’s thong, v-string or g-string underwear above the waistline of her pants, shorts, or skirt whenever she sits, bends over or squats, though some low-rise clothing is now designed to display the whale tail at all times; so-called because the strap closely resembles a whale’s tail rising from the water.
A whale tail is the effect that happens when a girls G-string or Thong becomes exposed as she walks, bends over or squats. Actually whenever you can see that wonderful exposed thong in the shape of a whale's tail. Lowrise jeans and higher cut thongs are creating for extremly great Whale Tails around as more and more thongs become exposed.
When Allison was bent over to tie her shoe her pink thong rose up and I saw a magnificent whaletail.