Contraction of the greeting "What's up?" which is a contraction of "What is up?" If you're really pressed for time, greet someone with a "sup"?. In any case, the greeter is rhetorically asking you what is going on in your life. Roughly synonymous with hello but less hip.

See also: Prepper | Dreamcreep | False flag | Asain | Dropping a deuce

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