A (traditionally) masculine man or woman, and especially a masculine lesbian. Often the "dominant" partner in a lesbian relationship, and especially of a butch/
femme lesbian relationship.
Dressing masculinely does not make a woman into a lesbian, contrary to popular belief; it's usually more
convenient.
Acting masculinely only means that's the gender role that the person identifies with; it has nothing to do with their sexual life. A highly masculine man could be
gay for all we know and a very feminine man could be straight for all we know, and both of these cases are frequent.
Long,
frilly dresses? Hair swept into a bun? Makeup?
Silks and satins? Sweet, shy disposition? Definitely a
femme.
Short hair? Denim? Leather jacket? Nose piercings? Motorcycles? Suits and ties? Loud and aggressive? How could that be more butch?