It is called the L-cut. You can learn it on the XCM world Champions DVD along with other moves such as juggling playing cards ,Pressure cuts ,and Armspreads.
or you could do the smart thing and get Jerry's Encyclopedia of Card Flourishes and learn enough material for the rest of your life including the L-cuts and much much more
I will personally agree with joshrobarts because, as well as the L-cuts, Jerry's Encyclopedia has tons of information on XCM and Cardistry that will allow you to learn so many spectacular stunts with cards that will amaze everyone. One of the greatest investments in Flourishing ever!