It’s pretty interesting how “concentration camp” used to just mean “a camp where people were grouped together”. It wasn’t necessarily pleasant, but in many cases it was effectively a relatively nice prison. Then, it became a euphemism for an extermination camp. The Nazis pretended they were just grouping people together in a camp, when in reality the aim was to kill everyone there. That euphemism tainted the original meaning, so now when people hear “concentration camp” they think of the Nazi extermination camps.

Technically, Guantanamo Bay probably qualifies as a concentration camp, but I bet they are very careful not to ever use that term.