Slang is a casual use of language that consists of expressive but nonstandard vocabulary, typically of arbitrary, flashy and often ephemeral coinages and figures of speech characterized by spontaneity and sometimes by raciness. The central characteristic of slang comes from the motive for its use: a desire for novelty, for vivid emphasis, for membership in a particular group or class of people whose "community argot", may be incomprehensible to an outsider, or for being up with the times or a little ahead. For example, crib—cheat in students’ slang, contract一order to kill someone.