COF, short for "Cum On Face," is a term used in the adult industry to describe a specific sexual activity. It refers to the act of ejaculating on the face of the advertiser. This activity is consensual and involves the advertiser allowing their partner to release semen onto their face. COF is a form of sexual expression that some individuals find pleasurable and exciting. It is important to note that engaging in any sexual activity should always be based on mutual consent and respect between all parties involved.