Metaphysical poetry came out of 17th century England. It is characterized by strange conceits (comparisons), images, or paradoxes (seemingly contradictory statements that actually have truth to them). Often centering on love, religion, or morality, these types of poems offer a logical or philosophical argument. Therefore, the poet will weave in comparisons that seem very out of place. However, once analyzed, these images or conceits do somehow relate to the poet's overall point.
A great poet to read is John Donne. Known as a highly religious poet, Donne has written quite a few metaphysical poems. One of his most famous is "A Valediction: Forbidding Mourning." Donne weaves in an extended metaphor of a mathematical compass as the speaker tries to convince his lover that his leaving is only temporary. The speaker refers to the compass to prove that he will return because their love is true.