Shoujo manga is a subset
proper, which are Japanese comics
. Shoujo is Japanese
", so you've probably figured out that shoujo manga are comics for girls.
This field alone is vast, but some of the better known titles (in the US, anyway) are Sailor Moon, Fushigi Yuugi (Also known as Mysterious Play), X 1999, and a handful of others, but this does not offer a very good representation of the themes shoujo manga often adresses.
Very often, shoujo manga deals with the intricacies of romantic relationships in every imaginable form, with male/male romances having their own subgenre called shounen ai, literally, boy love.
As a rule, shoujo manga is considered more literate and intelligent than its male counterpart, shounen manga. The artwork and page layout of shoujo manga tends to be more free-form than other types of comics, evoking subtle emotions in many ways.
The social contexts of shoujo manga are fascinating, but they can be tackled by some more ambitious person than me.
For those interested in Shoujo Manga but lacking the requisite knowlege of Japanese to read it, I recommend the following translated titles, hopefully available through your local comic store.
- Promise, by Keiko Nishi
- Magic Knight Rayearth, and anything else by CLAMP
- Fushigi Yuugi by Yuu Watase
- They Were Eleven, and anything else by Moto Hagio
- Strangers in Paradise, here because it's the only American comic that fits the above description, and has an interestingly large female reader base compared with other American comics.
- Manga! Manga! The World of Japanese Comics, by Frederick Schodt
- If you're willing to brave the weird typesetting, graphic design, and translation, you can try Card Captor Sakura, Sailor Moon, or Peach Girl, all available from Mixx publishing.
And, for those of you willing to find English scripts on the net, or with good working knowlege of Japanese, some other recommendations:
I feel it's important to mention something here: the few recommendations I've listed are an embarrasingly small and biased selection from manga that can be called "shoujo". So even if you don't like any of these, don't write the whole field off. Because Japan publishes a staggering amount of manga, and a big chunk of that is "shoujo manga". So you don't have to take my word for it