Cultural Marxism is a term that originated in the early 1970s by a scholar, Trent Schroyer in 'Critique of Domination The Origins and Development of Critical Theory' Schroyer used the term in an accusatory thesis correctly stating that many 'critical' theorists were failed Marxists, or cultural "Marxists" who had been absorbed into middle class capitalist society.
The above statement makes little sense unless you understand what 'critical theory' is, in the context that Troyer used it. In political philosophy, critical theory is a neo-Marxist philosophy developed by a nefarious group known as the Frankfurt School. It was initiated in Germany in the 1930s based on the philosophy of Marx and science of Freud. It is a melding of Marixst Fascist Socialism and Psychology.
Nearly everyone with the exception of the most oblivious dullards are well aware of what Marxism is. The simplest explanation being a debunked theory of scientific socialism, class warfare and class struggle, and a dictatorship of the proletariat. This Dictatorship of the Proletariat awaiting the arrival of of the fabled fools paradise of a classless society.
The economic aspects of Marxism are well documented lessons in abject failure, the principles he laid out along with his sidekick Freddy engles and Heirs Lenin, Hitler, Mao, Pol Pot laid waste to huge swarths of 20th Century History. Cultural Marxism like its evil twin Communism threatens the sancticty of society and could well be the harbinger that will lay waste to swarths of 21st Century History.
Advocates and Purveyors of cultural Marxism, well aware of the dubious reputation of their n'er do good ideology have chosen to conceal the Marxist connection. Make no mistake however, inside that trojan horse are the demons and demagogues of Marxist idiocy.
Cultural Marxism, along with its cousin National Socialism took form in ashes of post World War I Europe. Marxist theory had predicted that in the event of a sizable European war, the European working class would overthrow capitalism and bring about communism. Like most Marxist theories it fizzled and never materialized.
Marxist zealots were besides themselves and sought explanations as to why their Messiah had not delivered on his promise, the Revolution did not come as planned. The explanation they arrived at was that Western Culture, Religion and morality had distracted the proletariat from his true objectives as envisioned by Marx and that Western Morality, Culture and Religion were to blame.
In the early 1920s German Marxists established a think tank at Frankfurt University called the Institute for Social Research which would eventually become known as simply the Frankfurt School. At this 'school' they concocted their doctrine of cultural Marxism aka Critial Theory.
When those 'other Socialists', the Nazis came to power the Frankfurt School fled and landed right smack in the testicles of America - Columbia University, NYC
Having escaped the death camps of WWII these cultural Marxists shifted their attention to parasitizing their Host The United States.
One of the many treatises they shat onto the American Intellectual scene that was 'Critical Theory ' which is basically an outline encouraging criticism of every major institution - family, church, sexuality and so forth with the end goal of destroying them piece by piece. Some of their associated literature contains statements such as
'anyone who believes in traditional Western culture is prejudiced, racist or sexist or fascist - - and is also mentally ill.' 
Many scholars have noted that the Frankfurt School made extensive use of psychological conditioning. Today, when the cultural Marxists, who we now call cultural warriors and social engineers, endeavor towards an agenda such as promoting sexual perversions, or bringing down and denigrating a potential opposition leader such as Ronald Reagan or George W. Bush they do not argue the point based on its merit, they simply insert suggestions appealing to the anesthetized brains of the masses. They shoot television shows, commercials, propaganda masquerading as News, and a myriad of False Narratives at us.
Advocates of cultural Marxism prefer to distance themselves from their Marxist roots and prefer terms such as postmodernism, critical theory and similar quasi intellectual accolades. Many are simply sublimely ignorant useful idiots, wholly unaware the origins of their ideology and prefer to describe and think of themselves as social liberals.
Gay agenda, Feminism, multiculturalism, assorted shades of political correctness, are all well framed aspects of Cultural Marxism. The ultimate goal is to Destroy Western Civilization starting with its most stalwart defender - The USA, in order to bring out the fabled 'Proletarian Revolution' that their Demonic Messiah  envisioned.