T.S. Eliot first coined the phrase in his essay, 'The Metaphysical Poets' which was a literary criticism. The argument that he put forth was that cultivation of emotion and thought separately as divorced from one another was a broken way to deal with experiences that evoked both thought and emotion.
We may express the difference by the following theory: The poets of the seventeenth century, the successors of the dramatists of the sixteenth, possessed a mechanism of sensibility which could devour any kind of experience. They are simple, artificial, difficult, or fantastic, as their predecessors were; no less nor more than Dante, Guido Cavalcanti, Guinicelli, or Cino. In the seventeenth century a dissociation of sensibility set in, from which we have never recovered; and this dissociation, as is natural, was aggravated by the influence of the two most powerful poets of the century, Milton and Dryden (Eliot, "The Metaphysical Poets").