(1) The result of gate crashing a "shindig";
(2) Small to medium majorly drunken get together (mainly goon and cheap beer) before going out somewhere expensive because no one has money to buy real drinks;
(3) The revival of a shit party which no longer deserves the title of "party" after being shit but has SOMEHOW got good again so is a "Shang bang"; or
(4) Anything you want it to be