1. Someone who is addicted to sex, meaning they physically and mentally cannot go a certain amount of time without it. Usually results in having sex with someone they normally wouldn't, simply because they need a fix. Similiar to alcohol and drug addiction because in all three, a person is craving a release from stress and/or some form of gratification.
2. A lame reason people give for cheating on their significant other.
1. "I can't believe I had sex with HIM last night...he has every STD known to man, and a few known only to dogs. I felt the need to jump SOMEONE, and he happened to be right there. I hate being a sex addict."
2. "Baby...it wasn't my fault I slept with your sister...I'm a sex addict...I can't help it.."