What is a Mixed Economic System?

A mixed economic system has elements of both capitalism and socialism. A mixed economic system protects private property and enables some economic freedom in capital allocation, but it also allows governments to intervene in economic activity to achieve social goals.
Mixed economies, according to neoclassical theory, are less efficient than pure free markets, but proponents of government intervention argue that the fundamental conditions for efficiency in free markets, such as equal information and rational market participants, are impossible to achieve in practice.

A mixed economy is a mix of capitalism and socialism.

Anyone who says “that’s not really socialism cuz you don’t understand what socialism is” should use their own logic to figure out that it’s “not really capitalism” either. Or they could realize that neither definition requires that they exist in a vacuum. In the U.S.: capitalism exists and socialism exists. And the economy as a whole is neither. It’s a mix.

And anyone who says that government regulation/control is not “really” socialism because government is not the nominal “owner” needs to get their head examined. In this context, it’s relevant who exercises control, not whose name is on a deed. Again, when something is partially controlled privately and partially controlled politically, it is neither purely capitalism or purely socialism. It’s obviously partly both.