A butch* who is stone is one who prefers not to be touched sexually in a feminising way.
As with butches in general, stone butches may also be transgendered female-to-male or genderqueer and use male, female, or gender-neutral pronouns. In fact, anecdotal evidence suggests stone butches are much more likely to be transgendered than identify as women.
If not celibate, stone butches might take as lovers anyone, including men, but more usually women (often femmes) and other butches. Women who are attracted to stone butches and who are femme, may sometimes call themselves stone femmes.
To be stone is not foremost a lifestyle choice, but often a stone butch will find hymself involved in specific sexual and political dynamics, including butch/femme, dominant/submissive, daddy/girl and daddy/boi, queer politics and transgender politics.
Sometimes FTM men, particularly those who have lived as lesbians, may also use 'stone' (without 'butch') to describe their sexuality.
*Butch: a person who, having been identified female at birth or having transitioned to female, is masculine in appearance and/or identity, and usually also identifies as queer, bisexual, dyke or lesbian (or otherwise is attracted to female persons, although not necessarily exclusively).