Typically a middle-aged person who works 9am-5pm Monday through Friday at their job every week. They have never worked a weekend. A nine to fiver usually has a high-end office job. Also see: yuppie or weekend warrior
Nine to Fiver: Awww yeah! TGIF! Out comes my inner weekend warrior!
Weekend Worker: Man, f*ck you. I gotta work 'til close all weekend.
Nine to Fiver: *Giving the weekend worker the middle finger while driving away in his BMW*