A pair of sheets you specifically put on top of the bed prior to sex to avoid later sleeping in your own jizz. There are no specifications of sex sheets, though they mainly a light color to mask sex juice.
Also helps pass black light tests.
Hey What the Fuck, friends don't let friends sleep in other friends Jizz..... No worries, I had the sex sheets on first
Bed sheets on which some sexual act has occurred.
Sid had been sleeping in his bed for a week before he realized that it was covered in sex sheets; he immediately rinsed himself in acid and burned the sheets.