A concentration camp was a place where persons were kept imprisoned, usually for political reasons. Here they would labor and live, sometimes for years. The first modern use of them was by the British in the later stages of the Boer War (1899-1902) in South Africa, when confronted with determined guerrilla warfare by the Boers. In order to end this guerrilla war, they rounded up the Boer civilians (mainly women and children), burned down their homes and sent them to camps. (The purpose of this was to make sure that the guerrillas had no shelter or support). The camps were badly run, soon became overcrowded and insanitary. About 20% of the inmates died of disease within two years.
Similarly, many persons died in the German run concentration camps. It is not healthy to have many persons in cramped quarters for long periods. Even if food and medical care are plentiful (and they were not) - many deaths will occur. The USA also ran concentration camps for the Japanese. America, being a wealthy nation, gave relatively good rations and medical care to the Japanese. There was no forced labor either. The camps were cramped but not overcrowded compared to those in Europe and Russia and thus the mortality rate was much lower.
Contrast this with an extermination camp. Only Germany and Russia had such camps to my knowledge. Here persons were sent to die and die quickly. In Germany most were gassed, others killed by overwork or other means. In Russia the main methods were by forced hard labor, poor diet and extreme climate.
Technically all camps were within the concentration camp system, there were labour camps, transit camps and extermination camps. Concentration camps were generally intended for civillians, initially just for criminals, but gradually more types were included. Extermination camps were established about seven and a half years after the first concentration camps. They were much smaller than the average concentration camps (Auschwitz is an exception as it was both), as they only held enough inmates that were needed to opperate the gas chambers/vans and the cramatoria.