You're all good, I was skipping over the specific actions they list as being genocide but it is a bit unwieldy so I trimmed it down to "certain acts" make my reply a bit more concise.

The full text is

Genocide means 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.

So by forcing a group to transfer their children to another group (e.g. stealing the kids of one religion and relocating them to a different religious group or taking the children of indigenous peoples in Canada and putting them in residential schools) you are cutting the children's ties to their group of origin, which is basically to crush their cultural heritage and/or to "breed them out".

If people aren't allowed to propagate their cultural heritage and pass it down to their children, with things like language and food and dress, then it's a way of doing genocide by less direct methods than straight-up killing them because the intent is to take a race of people and, perhaps in a generation or two, to have people with black skin who are culturally entirely the same as the white population, for example.

Same for taking their kids and putting them where they aren't going to procreate with someone from within their own group - you aren't killing anyone but you're essentially diluting their ethnic group out of existence.

It's worth mentioning that this usually happens in tandem and not in isolation.

The UN definition of ethnic cleansing doesn't actually exist under that name but it's known as the crime against humanity of deportation or forcible transfer of population. (This also explicitly refers to forcible displacement.)

This is where it gets confusing and the media and mainstream discourse makes it even more confusing.

So you know how "purges" mean expulsion from the party in a formal sense, almost always in reference to communist parties, but people talk about purges in the sense that it's a euphemism for being executed by the state?

Ethnic cleansing is one of those terms. Some people who were purged were also executed but not all of them.

Ethnic cleansing often happens under conditions of war or civil war, but not exclusively. What this means is that, like with some purges, you can get a lot of killing or death and these deaths are used to ethnically cleanse an area by making the rest of the group flee, or an area gets ethnically cleansed and then direct evidence of genocide is established later on. You also get an ethnic cleansing that itself causes mass deaths thus also making it genocidal, like the Trail of Tears. So in effect people hear ethnic cleansing alongside genocide so often that it blurs and becomes a sort of euphemism for genocide. Which tbh is pretty understandable.

When is an ethnic cleansing not a genocide?

So that would be where a government rounds up the people in an area and forces them to leave their homes or territory but without killing them, to give a simple and straightforward answer. (But it could mean something like cutting off a water supply to a region so that the people are forced to move.)

It gets more hypothetical because the definition of genocide per international law doesn't set a number of deaths that you need to achieve before you are committing genocide but rather it looks at intent and action, and most historical examples of forcible transfer of population come with deaths as some people choose to resist which leads to killings. So if the government says "Clear the lot of them out, kill them if you have to" to the military or the police or a group like paramilitaries or gangs and they resort to killing some of the people who are being forcibly relocated then that's going to qualify as genocide.

If the government says "Clear the lot of them out but don't kill them" and one or more of that group resist and die in the process due to use of force then it's forcible relocation but not genocide. (Unless there's an order given by the leader of the forces and it can be established through witness testimony or some other evidence, then that leader is guilty of genocide but the government that issued the order to forcibly relocate them is not.)

A lot of this comes down to how the law functions.

If you have a law for murder but you don't have one for manslaughter then a lot of murderers will get off free because there's insufficient evidence to establish that the killing was premeditated, even if it was actually premeditated.

If genocide includes ethnic groups but it excludes religious groups then you're creating a legal loophole where a government can say "Kill all the... Muslims" and then when they get brought up on charges in the ICC they can show all the evidence that they never meant to kill all the Arabs (wink, wink) - it was just all the Muslims!

If the definition of genocide requires that a government issues the orders to the military then governments will just use paramilitaries instead and they'll use the loophole. Or the government will issue orders to the military by saying "I don't want a single person from that group left in that region" and the government won't be liable for actual genocide, even though the military is going to do what the military does and shoot people, so without having forcible relocation as a sort of back-up "manslaughter" charge then the government will get away with it.

This also explains why there aren't specific numbers attached to genocide or forcible relocation - because if it was set at 500 then governments would issue an order but limit it to 450 people and then the government would smile coyly and shrug their shoulders at the judge.

Often things like genocide can be extremely difficult to establish evidence for, or at least they used to be before modern technology. There might have only been footage of an armed group killing one single person before the person with a videocamera fled or was knocked to the ground but that footage along with the testimony of survivors might be deemed sufficient as evidence of genocide because the court can directly link one death of the targeted group to whoever carried out the genocide.

I hope that makes more sense now.

It gets really, really specific and intensely debated. This is also why I haven't dug deeper into the details because you could bathe a group of Muslims in pig blood for example and, if you go into the elements of genocide by by causing serious bodily or mental harm, as the UN defines it, then you're probably getting really damn close to the mark without actually killing a single person especially if it's done repeatedly or it's part of an established and proven pattern of inflicting mental harm on that same group of Muslims or other Muslims.

Like it or hate it, this is why there's so much work that goes into writing laws and interpreting laws and enforcing them. This is why legal studies and religious studies exist - you start with a simple law or commandment like "Do not kill" and then it becomes:

"...humans"

"...except in self-defence"

"...unless you used unreasonable force"

"...or if you had reasonable suspicion to believe that your life was under imminent threat, even if it is proven to be false later like if they convinced you that they were going to stab you but they were concealing a stick to make it look like a weapon"

"...or in war"

"...or if you are killing someone who is in extreme suffering that cannot be reasonably expected to be relieved"

"...except if they don't want to die"

"...except when they are unable to express their desire to die but their extreme suffering can be proven"

"...unless the person intended to cause harm to others by killing that person who is in extreme suffering"

"...or if there is a prohibition on killing that person (see: other law/religious edict)"

And it just goes on. And on. And on.