Neoliberalism is an economic term that refers to a modern (neo) version of liberal (laissez-faire) capitalism, as opposed to the Keynesian model that dominated much of the 20th century, following the classical period.
Although it was introduced many decades earlier, neoliberalism became a prominent school of thought in economic circles during the 70s, preaching a return to "free-market fundamentalism" through "limited government." It became the official federal model/agenda under Ronald Reagan, who was heavily influenced by neoliberal economist Milton Friedman. Reagan sold it to Americans by promising to "get government off our backs" and allow corporations to keep more money, which would in turn create jobs and trickle increased profits back down throughout the population.
Neoliberalism is defined by lower taxes on corporations & the wealthy, free trade agreements (ie. NAFTA), deregulation, and privatization.
Neoliberalism has determined the "public agenda" since Reagan. Reagan, Bush, Clinton, Bush, Obama, and Trump all operate(d) under this agenda, as determined by neoliberal orthodoxy and the military industrial complex.
With its conscious and deliberate shift in policy/philosophy that sought the proliferation of a "free market absent government interference," neoliberalism has created an environment ripe for corporate governance. And while capitalists, landowners, and the wealthy minority have always had a disproportionate amount of influence on the political process, the neoliberal agenda cemented a full-blown corporate coup in the US. It has been THE dominant model since, carried forward by both parties.