When somebody describes someone as "right-brained" they are describeing the person as creative and non-linear. The concept has it's origins in the reserch or Professor
Roger Sperry who, in 1947, did research where he cut the brains of some monkeys in half, sewed them back up, and then watched what they did. His
theory was that each side of the brain had distinct functions. Since each side of the brain is connected to one side of the body the idea of the experiment was that if you cut the part of the brain that lets the two halves talk to each other (the
corpus calosum) each side of the body wouldn't be able to do certain things. The problem with the experiment, and he says this himself in the paper, is that he was wrong. Each side of the brain is completely independantly functional, the only difference is that arbitrarily one side of the brain is better at some things than others. It's not necissarily the left side or the right side that is better at any one particular thing.
Now that I've said all that you'd think I'd shut up about it. Unfortunatly, that's not quite the case. There's this other nagging little problem I have with all this. Ever since somebody took this theory out of context and started this common misconseption (This person is Betty Edwards, who wrote the book Drawing on the Right Side of the Brain in 1979) people have begun associating activities with "right-brained thinking." These activities are typically artistic things like playing an insturment, or drawing. Now, even if Sperry had turned out to be right, learning how to do these things would still be a "left-brained" activity. When you learn how to draw, or play an insturment, or <insert your favorite stereotypically artistic activity here>, you learn the techniques in a logical and technical way. It's only when you use the skill later in an artistic fassion that it would be a "right-brained" activity.
This entire rant is particularly pointless, since once something becomes cliche it can never be undone, but at least it qualifies as Unsolicited Trivia.