I'm guessing it is a woman with low hanging or puffy mounds on her puss, showing cameltoe without cloth wrapping it.  Or maybe it is dry humping the clothed cameltoe or nude cameltoe.  Riding the crack, so to speak.

I too think it might have meant what is sometimes called a 'slide and glide', i.e. sliding your non-covered erection up and down between her pussy lips without penetrating her...  

It can be very erotic but also risky from the viewpoint that it can easliy lead to BBFS if each gets hot and bothered by this action...