Prostitution is the business or practice of engaging in sexual activity in exchange for payment. The definition of “sexual activity” varies, but it is often defined as an activity requiring physical contact (e.g. sexual intercourse, non-penetrative sex, oral sex, etc.) with the customer. The requirement of physical contact also creates the risk of transferring diseases. Prostitution is sometimes described as sexual services, commercial sex or, colloquially, hooking. It is sometimes referred to euphemistically as "the world's oldest profession" in the English-speaking world. A person who works in this field is called a prostitute and is a type of sex worker.