Halacha regarding modesty and community customs dictate the dress code for women. This "code" is practiced primarily by Orthodox Jews. Typically, women are expected to wear sleeves extending at least to the elbow, blouses or dresses with necklines that do not expose any cleavage and skirts long enough to cover the knees when seated.
Pants or slacks may be allowed in certain instances. For example, in many religious kibbutzim the women wear pants out of habit, for the simple reason that they work in agricultural areas or perform other activities where a skirt would be less modest. This is the exception; however, when not performing these activities, skirts are worn.
In addition, it is considered a breach of modesty for a married woman to have uncovered hair while in the presence of men other than her husband. Customs differ as to how much hair can be showing beneath the head covering, or if a wig is better or worse than a hat of some sort.
Unmarried women are not required to cover their hair, although there are Sephardic customs that even unmarried women should "put their hair up," so that it's not flying "wildly."