The pin of light you can see on a girl between the thighs and right at the vag. The light you hope to be able to see, because you know a number of things from the existence of that light:
1. She's at the very least in shape where it matters most
2. The area is properly ventilated
3. It's going to be tight
This term predates the misinformed "thigh gap" as it is preferred to have the thighs touch towards the top but have that pin of light exist. It has become lost knowledge that must be re-released to the masses.
You see that girl in the stretchy sweatpants walking away from us? Look at the top of her legs. You see that light at the end of the tunnel?
And dying in yo' bed many years from now, would ya be willing ta trade all da days from dis here day ta dat fo' one chance, just one chance, ta come back here as young men an' tell our enemies dat dey may take our lives but dey will never take our freedom ... YUB NUB!