Someone who has sex on camera for money. More often than not it is a person who had a terrible childhood, probably consisting of drug ridden and/or abusive parent(s) or being the victim of numerous rapes. They use sex to fill the empty void in their life because they have no other way of gaining satisfaction. Some people like to argue its normal because sex is natural, but these people are morons who should be sterilized for the benefit of all humanity. They fail to understand what effect psychology has on human sexuality because, as stated in the previous sentence, they are complete idiots and should be sterilized against their will. Or killed. Preferably killed so people like me don't have to know they exist.
Porn stars like to pretend their life doesn't suck, but in reality they have incredibly low self esteem and are mostly drug addicts. How fortunate for them we live in a completely idiotic society that thinks their behavior is normal.