A lesbian was a female homosexual. A common stereotype for lesbians was short hair. (PROSE: Revolution Man) Homo- and lesbophobia were a huge issue in human culture before Bernice Summerfield's home era of the 26th century. By Benny's time, though she couldn't understand why people had made such a big deal of such things. (PROSE: Sky Pirates!)
Even by 2030, though there was an air of passivity, at least among some. Fiona, or Fee, commented, "Fine, if that's what turns then in," after being told two women were lesbians. (PROSE: Warchild)
According to the thoughts of a man using a telephone, as taken in by Toshiko Sato with the telepathy pendant, Marcus Farrer had sex with two lesbians. "How would it work? I mean, does one of them sort of have to sit..." (TV: Greeks Bearing Gifts)
Charles "Chick" Peters specifically did not identify as a lesbian, despite his "female" body and attraction to women, because he identified as a man. Chick was in fact born with XY chromosomes, and did not have a womb. (PROSE: Blue Box)