What do the letters OC after someone's name mean?

The OC is a drama which revolves around the turbulent lives of four teenagers and their friends and family, who live in the wealthy seaside community of Newport Beach, Orange County, California.

The shows starts with Ryan Atwood, a troubled youth from the "wrong side of the tracks" being arrested because he stole a car with his older brother. After he is arrested he is saved by Sandy Cohen, a public defender. After Ryan's mom kicks him out the house, Sandy takes him back to their mansion in Newport Beach, where he would eventually be taken in by the Cohens for good.

There he meets Seth Cohen, an awkward yet funny geek who Ryan quickly befriends. He also meets Marissa Cooper, the pretty and popular girl-next-door who he develops a crush on. Their relationship only develops after he gets rid of her mean boyfriend, Luke Ward.

Summer Roberts is at first a dumb airheaded girl who just likes to party, but through much of the series she is shown to be clever and funny just like Seth, which is why they became the OC's super-couple.

The parents are not without their drama too. Kirsten and Sandy Cohen go through cycles of quarreling and making up, and Julie Cooper, Marissa's mom, is a sneaky gold-digger.

This sets the stage for quite a good show. It premiered on Fox in 2003 and ran for four seasons before ending in 2007. While the show has since been canceled you can still watch reruns on SoapNet (in the US)