Harem pants are trousers that are baggy in the legs but tight at the waist and ankles. They are supposed to have been worn by women in a harem in the Ottoman Empire. In the harem, or Western fantasies of harems, they can be see-through, although ones for everyday wear are opaque.
At various times (by feminists ca. 1850, by fashion designer Paul Poiret ca. 1910 etc.) there were attempts to introduce short skirts over items similar to harem pants (see bloomers) as an alternative to the long cumbersome skirts of Victorian and Edwardian clothing. The idea was that the loose (non-shape-revealing) covering of the woman's legs would appease modesty concerns, but critics considered any form of trousers worn by women as inappropriately masculine, and such styles never achieved mainstream acceptance (though some women's bathing suits were constructed along similar lines).