Socialism is an economic system based on government control of the means and outputs of production – usually through regulation or ownership. As a practical matter, “socialism” runs on a continuum from government regulation to internalize externalities through total government economic control.
I do not universally conflate economic policy with social policy in this definition. The rule of law and consistency in approach and effective governance of the people, limited size and scope of government, high regulatory efficiency and open markets are all indicia of a well functioning free market – the economic opposite of pure socialism where the government has total economic control.
Any study of economic history shows that the more distributed the economic power, the more effective the economy functions. Concentration in the hands of a few (be those oligarchs or the state – both usually supported by the governmental and regulatory environment) is economically inefficient. The US is more socialistic than those states because the government and regulatory structure is used to concentrate the means of production through bias in tax policy (think loopholes), government spending (think military spending and targeted stimuli), tax burden (think control over labor outputs ad tax structure), property rights (regulation to prevent competition, patent rights, non-compete agreements, ability to build and develop), statutory bias (think some of the laws to protect banks against borrower lawsuits, tort limitations, cost and complexity of lawsuits, lobbying).
You want a simple definition, but no good one exists. But the closer you get to government control over the means and outputs of production and the concentration of power in the hands of a few – whether elected officials, bureaucrats, capitalists or anyone else – facilitated by government policy – that’s socialism. And we DO live in a more socialist nation than some you may believe – but the government power is leveraged by private individuals for economic gain.