In English informal speech, a French kiss, also known as a deep kiss or a tongue kiss, is an amorous kiss in which the participants' tongues extend to touch each other's lips or tongue. A "kiss with the tongue" stimulates the partner's lips, tongue and mouth, which are sensitive to the touch and induce physiological sexual arousal. The oral zone is one of the principal erogenous zones of the body. The implication is of a slow, passionate kiss which is considered intimate, romantic, erotic or sexual. The sensation when two tongues touch, also known as "tongue touching", has been proven to stimulate endorphin release and reduce acute stress levels. French kissing is often described as ‘1st base’, and is used by many as an indicator of what stage a relationship has reached.
