Casual sex
The term 'casual sex' implies there's no commitment to the other person. Although this doesn't necessarily mean there's no sense of responsibility or care, in a casual encounter you're more likely to focus on the here and now. You can enjoy the moment without much thought about what your partner thinks of you or what you think of them. Without the emotional complications of a relationship, you're free to concentrate on physical satisfaction.
Sex with a stranger - for many people, unfamiliarity is the key to casual sex. They find the mystery exciting and, if there's no chance of meeting again, inhibitions can be cast aside. It offers the chance take on a new identity and act out a secret fantasy with little fear of rejection.
Element of risk - danger is generally part of casual sex. There's a sense of being naughty, of tasting the forbidden fruit. Some people deliberately add to their sexual encounters by choosing public places or partners they feel should be off-limits.