This term is evolving as a bifurcation of the term 'giving head', which could mean performing oral sex on either males or females, but more often referring to fellatio, oral sex performed on males. The newer term 'giving face' is now tending to a more restrictive meaning of cunnilingus only, or oral sex performed on females, and 'giving head', towards only fellatio, or oral sex performed on males.
Neither term differentiates between which sex is performing the sexual act; only the sex of the recipient is relevant.
When you bury you face in a beautiful woman's pussy and gently stimulate her vagina until she cums.
Fred: Dood my girlfriend left me cuz I wouldn't give her face
Doobie: Dood that sux.
Fred: I'm so depressed, I just wish I knew where she was.
Doobie: I'm pretty sure she's still asleep in my bed. Her cunt tastes pretty good.