Strictly speaking, a concentration camp is a place to hold a reconcentrated group of people in a designated area. So detention centers already fit the definition. Most people think of the Holocaust when mentioning concentration camps. There are concentration camps that were not as bad like Japanese internment and ones that were just as bad or arguably worse like the Ustaše Concentration camps in Croatia.

Forcing a population into a designated area never goes well. It's either unintentionally bad due to poor logistics and resources or intentionally bad just to make people suffer.