Someone who identifies as a woman, and is romantically and sexually interested in other women (that's the "lesbian" part) AND who dresses, acts, or speaks in ways that many people in society consider "masculine" (that's the "
butch" part). A butch lesbian is likely to feel more comfortable with short hair than long, and likely shops in the men's department a good chunk of the time. But, as with all identities, there are lots of exceptions.
Generally, butch lesbians do not want to BE men (women who want to be men are called
transgendered or
transsexual). Nor do butch women hate men, as it is sometimes thought. Many butch lesbians believe that men make terrific buddies (they just aren't interested in men as
bed buddies).
There are many kinds of butch lesbians. A few stereotypical types include "motorcycle butch," "sporty butch," and "metrosexual butch." More on these later, perhaps.