Revolution Gets Full Season Order

Only three episodes in and NBC has greenlit a full season order for JJ Abrams' Revolution. I am unclear what a "full season" means in this case as that number usually lands between 20-24 episodes. The initial order had been for 13 episodes of the show. The decision seems to be based on Revolution's viewership numbers of around 10 million, a number that few shows can get nowadays. The show also benefited from a huge 53% bump in viewership once DVR ratings are added (called Live+3 for air time plus three days after). Since most DVR users tend to be in the coveted 18-49 age range that advertisers love it scores the dual hit of strong ratings and happy advertisers.