The stories tend to be about everyday experiences of women living in Japan. Though there are some that cover high school, most cover the lives of adult women. The style also tends to be a more restrained, realistic version of shōjo, keeping some of the wispy features and getting rid of the very large sparkly eyes. There are exceptions in the style described above, but what defines josei is some degree of stylistic continuity of comics within this particular demographic (the same is true with different demographics that have different stylistic tendencies).
In addition, unlike shōjo manga, josei comics can portray realistic romance (as opposed to mostly idealized romance). A subset of josei comics are comics that are aimed at women about homosexual male relationships, much like but not to be confused with yaoi; josei tending to be both more explicit and with more mature storytelling. Josei is also known for a very sexual edge; many of the magazines have some of the raunchiest porn produced in Japan.
Josei is sometimes used within anime or manga, mostly by male characters, to refer to a sexual preference for older women, as contrasted with lolicon.
Examples
Blue
Gokusen (anime and manga)
Happy Mania (manga)
Tramps Like Us (manga) Japanese title: Kimi wa Petto
River's Edge (manga)
Honey and Clover (manga and anime)
Categories: Anime and manga terminology