Fun fact: What most people refer to as cinder blocks are actually concrete blocks.
Back in the day people burned coal to heat their homes and places like Bethlehem Steel had large coke ovens going 24/7, producing a a great deal of “cinders,” the term for the ash that has been left behind when coal or similar fuels are burned. A typical winter would leave a homeowner with numerous trashcans worth of cinders; and coal-fired power plants and steel mills would create tons of this waste every day. These cinders were used as the aggregate to make cinder blocks.
Concrete blocks are made of pure concrete. The aggregates used are finely crushed stone or sand. They are much stronger than cinder blocks, which haven't been mass produced in over 50 years