Literally means "maiden" in Japanese. It is also the partial name of a popular shoujo anime sequel: "Mai-Otome." The original being Mai-HiME.
The term "otome" is also slowly being integrated as a new way of referring to a ramped anime/manga fangirl. It's a more specific and updated version to the current otaku label (which has been grossly misinterpreted in the States).
"That girl's a MAJOR otome! She's got over 80 manga!"