I looked up degrees of cousinage (?) on Wikipedia once, but it didn't stick. Only now that I've seen this graphic I found over at lifehacker does it gloriously click. I'm going to share it with you now 'cause I think it's pretty slick.
And now I won't forget. The girl to the right (my left) in the photo above is my first cousin, once removed. Once removed simply refers to which generation the relative belongs. My first cousin, to the left, had a daughter, who is one generation removed from me. She's my first cousin, but once removed. Boom.