From Wikipedia: "In a free market, the laws and forces of supply and demand are free from any intervention by a government or other authority and from all forms of economic privilege, monopolies and artificial scarcities."

I think most people stop reading at "government" and don't realize that for a free market to exist, it needs to exist in a vacuum. There is no frictionless market, and every market has it's share of cost externalizations (plastics, energy, etc.), or leverage imbalance (healthcare, labor market).