A French kiss (or tongue kiss) is a romantic or sexual kiss that involves touching the tongue or lips of one's partner with one's own tongue. Often this involves inserting one's tongue into one's partner's mouth, or vice versa. French kiss is also known as tongue wrestling and tonsil hockey. In British slang, this type of kissing is commonly known as snogging.
People engage in tongue kissing, rather than simple kissing on the lips, in order to maximize the pleasurable sensations involved with kissing, and to heighten the sense of physical intimacy. While kissing on the lips can be associated to non-romantic, non-sexual relationships (e.g. mother/son relationship), a tongue kiss is almost always (at least in Occidental cultures) of a sexual nature.
Older books sometimes refer to this as a columbine kiss, i.e., after the manner of doves, or a soul kiss.
French Kiss is a 1995 movie starring Meg Ryan and Kevin Kline.