Before we start, some ground rules. For the purposes of this discussion, we will defer to the UN Convention on the Prevention and Punishment of the Crime of Genocide, effective 1951.
As to what we consider canon - while the movies always take priority, we will allow relevant EU sources.... any of the following acts committed with intent to destroy, in whole or in part, a national, ethnical, racial or religious group, as such:
(a) Killing members of the group;
(b) Causing serious bodily or mental harm to members of the group;
(c) Deliberately inflicting on the group conditions of life calculated to bring about its physical destruction in whole or in part;
(d) Imposing measures intended to prevent births within the group;
(e) Forcibly transferring children of the group to another group.
— Convention on the Prevention and Punishment of the Crime of Genocide, Article 2[5]
At first glance, it seems like a no-brainer. Order 66 explicitly about liquidating the Jedi en masse - going so far as to massacre the younglings. And while the Jedi are not a national, ethnic or racial group...they are a religious order. So at the very least we meet condition A, and possibly a great deal of C happened as well, given then everyone seemed to have largely forgotten the Jedi just a few decades later.
But on deeper reflection, I'm not so sure. It's a massacre, certainly, but that doesn't mean it's a genocide. A couple of things stand out to me.
Are the Jedi really a religion?
Well, they're monastic, certainly, and we tend to associate that with religion, but on closer inspection they don't really look like any religion Westerners are familiar with. The Jedi don't really worship anything, nor do they hold services or preach to the masses. They claim to serve the Force, but there's not really any faith involved there, because the Force is a quantifiable thing in the Star Wars universe. (Faith would be a lot easier if your local priest could levitate cars with his mind.) There are Jedi 'temples' but non-Jedi are not permitted access, and its not clear that there is any wider congregation. I'm not super familiar with Buddhism or Hinduism, so maybe there are some clearer parallels there, but either way, the fact that Jedi can force choke people whether they believe in the Force or not kind of moves them away from "religious order" in my mind.
There are no Jedi civilians.
Every Jedi - and I mean literally EVERY Jedi - is a super warrior, capable of taking on whole platoons of regular troops and emerging unscathed. In addition, Jedi are also minor telepaths, capable of reading surface thoughts and even mind controlling people for small lengths of time. There's no such thing as a "helpless" Jedi. Even Younglings are phenomenally dangerous - there have been documented cases of people with literally no force training whatsoever dominating minds.
Jedi are DEEPLY political.
Unlike most monastic orders that Westerners are familiar with, who attempt to turn their backs on physical world to focus on spiritual matters, the Jedi are at the very center of Galactic power. They are ostensibly servants of the Galactic Council, but they wield tremendous authority, and there are at least some areas where Jedi do not appreciate the Council's involvement. They are routinely dispatched as diplomats, generals, and...'peacekeepers.' And if they feel it necessary, they have no problem deciding to remove the duly elected chancellor from power....with a lightsaber.
Painted in THAT light, the Jedi start to look more like the Praetorian Guard than a religious order. And political purges, no matter how brutal, are not generally considered to be genocides. The French Resistance killed THOUSANDS of suspected collaborators after the war, the September movement massacred hundreds of thousands of communists in Indonesia, and of course, Stalin's Great Purge went well into 7 figures - but none of those are genocides per the UN definition. If my memory from Revenge holds up, the Jedi were liquidated after a failed coup attempt, which is not exactly an unusual response to that sort of thing.
But it's a been a long time since I watched Revenge and I know that a lot of you know a lot more about the Star Wars universe than I do....so....am I missing something?