We can hold Kimberlé Crenshaw (a “woman of colour”) responsible for the ugly word, 'intersectionality'. (She coined it in 1989.) The incredible thing is that she deemed it to be a "common everyday metaphor".

I'll let Crenshaw herself define the term. Thus:

“The view that women experience oppression in varying configurations and in varying degrees of intensity. Cultural patterns of oppression are not only interrelated, but are bound together and influenced by the intersectional systems of society. Examples of this include race, gender, class, ability, and ethnicity.”

What we have here, essentially, are various (Leftist/ “progressive”) movements and individuals trying to discover -- or invent -- yet more minorities to exploit for their own political/social ends.

Thus today we have to take on board the following identities and backgrounds: cisgender (female/male at birth, and still identifying as female/male), national origin, criminal record, race and ethnicity, class/socioeconomic background, ideology, religion, immigrant status, refugee status, body type, educational background, appearance... ad infinitum.

Some sorry souls are the victims of various “axes of oppression”. There are some people, for example, who are transgender, black, and poor. 

It's not always doom and gloom, however. Certain individuals will suffer both “privileges” and “oppressions” if, say, she/he is both middle class and black. Or, alternatively, if one is a very well-paid academic (say, researching into intersectionality) and also a woman, you'll be oppressed because of the latter category and privileged due to the former one.

Thus it can be the case that one's oppressions cancel out one's privileges. Or, alternatively, one's privileges can cancel out one's oppressions.

Marxism or Post-Marxism?

It's been said (by intersectional theorists and others) that in the old days (Marxist) activists didn't realise, for example, that black women are more oppressed than black men. Now, almost by definition, that's taken to be of prime importance. (See here.)

The Telegraph's (yes, the “Torygraph”!) very own intersectional theorist (an Ava Vidal) offers her own view on, for example, why traditional Marxist feminism wasn't radical enough. She writes:

“The main thing 'intersectionality' is trying to do... is to point out that feminism which is overly white, middle class, cis-gendered and able-bodied represents just one type of view -- and doesn't reflect on the experiences of all the multi-layered facets in life that women of all backgrounds face.”

What's more, Ava Vidal quotes someone saying that

“white feminists... refuse to acknowledge that they benefit from a white supremacist hetero-normative [sic] patriarchal system”.

Despite all that, Marxists have always been aware of “identities” other than that of class. Indeed, Marxists have been theorising about gender and race for decades. However, most Marxists have also stressed the point -- which they see as being of vital importance -- that it is class, and class alone, which gains a privileged place amongst these hierarchies of identity/oppression.

Thus intersectional theory is certainly “post-Marxist”, if that simply means Marxism + other theories. In other words, Marxist theory hasn't been forgotten. Intersectional theorists, for example, still highlight the fact that we all live within a “capitalist Euro-centred modernity”. Indeed, it's capitalism (or capitalist democracy) which accounts for the fact that people are, amongst other things, “raced and gendered”.

To highlight this Marxism/intersectional alliance, take these words from Revolutionary Socialism in the 21st Century; which is made up of former members and leaders of the Brtish Socialist Workers Party. (See here.)

Firstly, we are given reasons as to why intersectionality matters. Thus:

“... that one form of oppression can be shaped by and can shape other forms of oppression. Racism, for example, can be sexualised, or women’s oppression can be racialised – and this happens in such a way that it becomes impossible to view different oppressions as separate.”

But now we get to the prime and traditional bête noire of revolutionary socialism (if tinged with intersectional theory): democratic capitalism. Thus:

“We already know that all oppressions are connected by having material roots in capitalism. And by claiming that all oppression and exploitation intertwine, there is at least a vague recognition by intersectionality that all oppression is rooted in the same societal structures.”

And later we also have the following:

“Marx knew nothing of intersectionality as it exists today, but he speaks in similar terms in his sixth thesis on Feuerbach: 'But the human essence is no abstraction inherent in each single individual. In its reality it is the ensemble of the social relations.'...”

Finally, we have the same Marxist actually selling us intersectional theory again. Thus:

“... the way intersectionality is used today – for example on campuses... is as a call to unity! The argument is that everyone concerned with oppression should naturally be concerned with the nuances of everyone else’s oppression.”

So even though new genres have been introduced, class (though sometimes race) is still often still seen to be of prime importance.

Not that all Marxists are happy with intersectional theory and other “progressive” alternatives to pure Marxism. Take “the most well-known thinker of our time” (according to the Guardian) – Slavoj Žižek. In Contingency, Hegemony, Universality (2000), Žižek writes:

“... today's capitalism, rather, provides the very background and terrain for the emergence of shifting-dispersed-contingent-ironic- and so on, political subjectivities.”

Žižek then says that capitalism

“has created the conditions for the demise of 'essentialist' politics and the proliferation of new multiple political subjectivities. So, again, to make myself clear.... [capitalism] creates the very background against which 'generalised hegemony' can thrive.”

Let me put that in plain English:

Multiple political “subjectivities” are a problem for Žižek. He wants the working class as a whole to fight capitalism. Or, at the very least, Žižek wants all the other subjectivities to unite behind the “hegemony” that is the working class (if led by a middle-class university-based vanguard). This multiplicity of subjectivities and “hybrid identities” simply muddies the water that is the ancient (Marxist) class war.

You see, what the intersectional theorists, postmodernists, poststructuralists, etc. don't realise is that all this

“playing with multiple, shifting personas... [simply] tends to obfuscate... the constraints of social space in which our experience is trapped”.

In other words, all this “playing” still occurs within capitalist democracies.
Here are a few more minorities of identities to throw into the radical pot: people born on a Tuesday in June, serial killers, people with long fingernails, white upper-bourgeois academics who specialise in intersectional theory, black/ Muslim Uncle Toms and so on.

Indeed, I'll let the reader indulge in the possible juxtapositions or permutations of the following “oppressed groups”: the “transgendered”, black, gay, women, black gay, white working class, black working class, rich and ideologically powerful academics, etc.

It's complicated, isn't it?

Finally, here is some pious and righteous advice (from Geek Feminism Wikipedia) for all you evil white, cisgendered, racist, hetero-normalist, fascist oppressors out there:

“If someone suggests that you're doing something racist, ableist, etc., you will tend to react defensively. That's OK and natural! Take a deep breath, step away from the keyboard if you need to, think about the perspective of others in that situation, then apologise and figure out how not to do it again.”

And what can you say to all that?