Short answer: Estimates vary depending on how one counts, but most reputable sources place the figure in the tens of thousands of camps and related detention sites, with far fewer “main camps” and many more satellite, subcamp, ghetto, transit, and work camps tied to the Nazi system during World War II. Context and figures you’ll often see

• Main camps and subcamps: Historians distinguish “main” or “ Stammlager” camps from a vast network of subcamps. The main camps number around two dozen, while satellite/subcamps run into the hundreds or thousands depending on methodology. Different scholars provide slightly different tallies, reflecting evolving research and definitions. [historian-based estimates commonly cited in scholarly and museum literature]
• Total sites across occupied Europe: When including ghettos, transit camps, forced-labor camps, and other incarceration sites connected to Nazi policy, estimates reach into the tens of thousands. Some prominent sources describe roughly 40,000 or more total sites (including ghettos and other forms of confinement), with a substantial subset being concentration camps and their subcamps. [broad archival surveys and modern museum overviews]
• Concentration camps vs extermination camps: Extermination centers (e.g., Auschwitz-Birkenau, Treblinka, Sobibor, Belzec, Chelmno, and Majdanek) were a subset within the broader camp system. The overall system encompassed a range of purposes, from political detention and forced labor to mass murder. [specialized historical summaries]

Key distinctions to understand

• “Concentration camps” can refer to a wide array of sites used for detention, forced labor, and political repression. Subcamps and satellite camps were common, often attached to a larger primary camp. [scholarly definitions]
• “Extermination camps” (death camps) were specifically designed for mass murder and are a component of the broader system. They are frequently highlighted, but constitute only part of the entire network. [Holocaust scholarship]

If you’d like, I can pull precise, citable figures from current museum or academic sources and present a concise comparison (main camps vs. subcamps vs. extermination camps) with short notes on methodology.