River Song 

Played by Alex Kingston, River Song is the mysterious traveller of space and time who first appeared in the eighth episode of the fourth season of Doctor Who. River Song refuses to tell The Doctor who she is, saying she can't give him "spoilers". As of yet, who she is is still unknown, and fans everywhere have long speculated about her true identity. According to the writers of the show, this will be revealed in the sixth season.

River keeps a diary of The Doctor's life, which he isn't allowed to look at. She calls him "sweetie", which has caused viewers to wonder if their relationship goes beyond friendship. Since River and The Doctor keep meeting at different points in time and space, their timeline is rather messed up.

An example of her mysteriousness:

The Doctor: River... Who are you?
River Song: You're going to find out very soon now, and I'm sorry, but that's when everything changes.

River Song by Rosiepeverell April 11, 2011

River Song 

Verb
To watch the episodes of a TV series out of order, usually spoiling the story for yourself and sulking about it.

Derived from River Song, a companion (wife and killer as well) of the Doctor who met him in the wrong order all the time. Time travel does weird things, you know.

Jim: Dude did you hear, Jacob watched season 3 before season 2.
Craig: Damn man, he totally River Song-ed the series. Now he's going to go on about how everything was so predictable.

River Song by leodiction June 1, 2014