A group of 17th century English poets who wrote during the same time as the Cavalier Poets (the reign of Charles I, 1625 to 1649), but a very different sort of poetry.
They primarily wrote lyric poems, which were concerned with lofty and deep topics, and which, even when apparently more commonplace, frequently had a hidden meaning. John Dryden said of Donne, "He affects the Metaphysics ... in his amorous verses, where nature only should reign; and perplexes the minds of the fair sex with nice speculations of philosophy, when he should engage their hearts."
They were not mystics: they generally approached their topics in a logic manner, fusing reason and emotion. Nor was their poetry dry: it was positively raw (well, not really) compared with the average 16th and 17th century poetaster. Their poetry employed "metaphysical conceits"- complex metaphors that frequently had unusual dimensions. They were known for their intelligence and wit.
John Donne, Abraham Cowley, George Herbert, Richard Crashaw, Henry Vaughan, Thomas Traherne and Andrew Marvell are the best known metaphysicals.