What Are They?

Back Dimples are also known as: Sacral Dimples, Bum Dimples, Butt Dimples, Dimples of Venus or Pilonidal Dimples (Not sure about the last one though, I think that's lower down).

Back Dimples are, according to Wikipedia:

The phrase dimples of Venus refers to the pair of sagittally symmetrical indentations sometimes visible on the human lower back, just superior to the gluteal cleft. The dimples are directly superficial to the two sacroiliac joints, the sites where the sacrum attaches to the ilium of the pelvis.

This term, while informal, is a historically accepted name within the medical profession for the superficial topography of the sacroiliac joints. The Latin name is fossae lumbales laterales ('lateral lumbar indentations'--literally 'ditches' or 'trenches').

I'm not sure what much of that means & it doesn't sound that sexy, but, what I can make of it is, they seem to appear at the point where the back bone meets the hip bones. But to be honest, I think that's blatantly obvious!

Not everyone has them It is the general consensus that you can't exercise to get them. So if you do have them then I suppose you are just lucky.