Slang with engineers and drafters for a number with four zeros in a row which is typically found in a top level assmembly drawing. Originated with the aerospace industry back in the 50s. In nerdspeak it has morphed into meaning anything that describes the big picture or the master plan.
"Bob, have you finished the four balls for the flux capacitor installation yet? The PHB is down my throat and threatening to take my stapler if it isn't done by this weekend."

"Dude, what's the four ball on backpacking to the hotsprings this weekend? Your sister coming?"
by Sigmatero December 10, 2006
Two men riding together on the same motorcycle or scooter.
Fred: Hey man, can I get a ride on your new Harley?

Tim: No way!

Fred: Why not?

Tim: Dude, that's four-balling - and not cool, especially on a Harley!
by Pastcha July 28, 2014
A double banger. Police ambushing a house IE.. One bangs on the front door and one bangs on the back door.
MIKE: Fancy a FOUR BALL with her? DAVE: Yes! I'll bring up the rear.
by Deno February 22, 2005