a.)A lazy version of What is up?
b.)Yeah that's right

sup (query) bastardisation of the phrase "what is up" A lazy way of expressing the mind numbing boredom of unstructured young minds.

Short form of what’s up

What's Up

Yep, thats all

slang way of saying whats up

A text message you send to someone to let them know you want to talk by phone, but do not want to call the other person without warning, usually because of the time of day and the fear of outright assault by ones wife. Can be used alone as a single word or as part of a compound word with other words added to it, such as supdog, sup-per, sup-foo, etc.

Sup requires either a return phone call or a ready why the other party can't talk at that time. Ignoring a Sup is an indefensible violation of the bro code.