“Ethnic cleansing” sounds almost like routine maintenance, doesn’t it? Like you’re bringing in someone to shampoo the carpets or scrub under the fridge.
It means genocide, though. In case your Greek is rusty, genocide means killing a lot of people with the same skin tone or religion or accent or whatever because you’ve determined they are the cause of your problems.
If you were trying to get away with mass murder, you might tell people the whole thing was an exercise in “ethnic cleansing” to get them to think about disgusting but necessary household chores instead of thinking about how you are murdering people.