Gender was the concept of identity relating to whether someone was male or female, or masculine or feminine, although there was a diverse spectrum of gender identities. (PROSE: Island of Death)
The Tenth Doctor told Rose Tyler that the Time Lords considered concepts like gender to be archaic, (AUDIO: The Sword of the Chevalier) the Twelfth Doctor explaining to Bill Potts that the "most civilised civilisation in the universe" was billions of years beyond petty human obsession with gender and its associated stereotypes. However, she pointed out that they still called themselves Time Lords. (TV: World Enough and Time) Although "Time Lady" was also used, Missy considered the term "old fashioned." (TV: Dark Water
Later, while pretending to be the Doctor, Missy referred to Nardole and Bill as "Exposition and Comic Relief." When Nardole retorted that they weren't functions, she responded "Darling, those were genders." (TV: World Enough and Time)