The official name is Mahou Shoujo Madoka Magica. What is this "Puella Magi" bullshit? Is that even a real word?

http://www.animenewsnetwork.com/news...-madoka-magika

At 23:52 in the episode, Kyube clear says "...mahou shoujo..." but it got translated into "Puella Magi." WTF IS THIS?