In the
humanities and
social sciences, critical theory has two quite different meanings with different origins and histories, one originating in
social theory and the other in
literary criticism. Though until recently these two meanings had little to do with each other, since the 1970s there has been some overlap between these disciplines. This has led to "critical theory" becoming an umbrella term for an array of theories in English-speaking
academia. This article focuses primarily on the differences and similarities between the two senses of the term critical theory.
See more at Wikipedia.org...
Although the term is sometimes used more broadly, in most contexts it refers to the school of thought represented by the "Frankfurt School," which is a school of thought that combines psychoanalysis and Marxism.  A key text of this school of thought is
Adorno & Horkheimer 72