Aktion T4 was a campaign of mass murder by involuntary euthanasia in Nazi Germany. The term was first used in post-war trials against doctors who had been involved in the killings.[4] The name T4 is an abbreviation of Tiergartenstraße 4, a street address of the Chancellery department set up in early 1940, in the Berlin borough of Tiergarten, which recruited and paid personnel associated with Aktion T4.[5][b] Certain German physicians were authorised to select patients “deemed incurably sick, after most critical medical examination” and then administer to them a “mercy death” (Gnadentod).[7] In October 1939, Adolf Hitler signed a “euthanasia note”, backdated to 1 September 1939, which authorised his physician Karl Brandt and Reichsleiter Philipp Bouhler to begin the killing.

https://en.m.wikipedia.org/wiki/Aktion_T4

I hate the use of “euthanasia” and “mercy death”. This was genocide, perpetrated by nazi germany and nazi doctors.