Steven Muecke provides a description of what theory is in his review of Morton’s Hyperobjects:
What he does is “theory,” which is what high-flying professors of English write when they are not training people to read literature. Those who read Terry Eagleton’s Literary Theory in college will be familiar with the genre. It comprises difficult material made a little more accessible, and even enjoyable, via rhetorical flourishes, brilliant and breathtaking connections (Marx, God, Wordsworth, and cornflakes might appear in the same sentence), and sometimes it includes combat sports, as rival critical theories are pummelled into the ground.
Theory is not an academic discipline. Philosophers reading Hyperobjects might groan and protest (see Nathan Brown’s review of Morton’s recent Realist Magic), but Morton is not doing philosophy, he is sampling it. Likewise with the most recent advances in theoretical physics, appearing in this book in spades, along with some writing about avant-garde arts and music. It’s a strange mash-up, this theory stuff. You don’t read theory to advance the discipline you might belong to — you read it for stimulation…