Definition of "undesirable"

There would be no need for any of the animals to come in contact with human beings, which would clearly be most undesirable.

1945 August 17, George Orwell [pseudonym; Eric Arthur Blair], chapter 6, in Animal Farm […], London: Secker & Warburg

Chronic venous disease includes cosmetically undesirable telangiectasias, varicose veins, venous ulceration, and claudication.

2008, Mary E. Klingensmith, The Washington Manual of Surgery, page 327

[David] Brog spoke movingly of his immigrant grandfather as a triumph of the assimilationist model—a Romanian Jew who emigrated to America, learned English, and became a good patriotic American—but failed to mention that the 1924 Immigration Act was designed specifically to exclude Eastern European Jews (among other undesirable European ethnic groups) from entering the country.

2019 July 24, David Austin Walsh, “Flirting With Fascism”, in Jewish Currents‎

Barskiven Road was The Undesirables. Bad corporation tenants (didn't pay their rents, didn't dig their gardens, let their kids smash up windows) were transferred to The Undesirables until they showed they'd improved. His mother called them scum. Barskiven Road houses had all-metal fittings. Only the window panes could be broken, unless you had a blow-torch. McCann said they'd have them, soon. At the dancing blokes always made jokes if they knew a dame was from The Undesirables. It was supposed to be the worst street in the whole of Kilcaddie.

1968, Gordon M. Williams, From Scenes Like These‎, William Morrow and Company, page 121