I was able to learn a tiny bit of the Japanese language through a project I did, which all of the seniors in California have to complete in order to finish high school. They could make their own topic, so I did mine on the history of comics and making a comic book, and I learned through studying manga that "shoujo" means little girl. This usually applies to teenage girls, but it can range from toddlerhood to late teen. "Bishoujo" means pretty girl.
Here's a TV tropes article that gives a better description. Alternatively, "bishonen" means pretty boy. It's just that a lot of the looks of the characters in the anime fit that bishoujo and bishonen trope.