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!)
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)
According to one account, Iris Wildthyme was a lesbian novelist from late 20th century Earth. (PROSE: Hospitality) In a universe where she was a Time Lady, Iris had a lesbian companion named Jenny Winterleaf. She described her to the Third Doctor as "the butch dyke traffic warden". (PROSE: Verdigris)
Bill Potts, a companion of the Twelfth Doctor, was attracted exclusively to women. (TV: The Pilot, Knock Knock, Extremis, The Eaters of Light) She eventually ended up with a girlfriend, Heather. (TV: The Pilot, The Doctor Falls)
Behind the scenes
In their audio commentary on Forest Of the Dead), Russell T Davies and Steven Moffat revealed that Lee McAvoy (who appeared as a man marrying Donna Noble within the Library) was a woman in the real world. However, they cut it for fear that the reveal would be too confusing, as too little had been done to establish the possibility of characters looking different outside the simulation from how they did within it.
Fanart reposted by the official Doctor Who Twitter account for #FanArtFriday on 3 June 2022 depicted Yasmin Khan with face paint of the lesbian pride flag as well as a pin of the flag's colours in the shape of a rainbow.