Iambus n. : A foot consisting of a short syllable followed by a long one, as in /mans, or of an unaccented syllable followed by an accented one, as invent; an iambic. See the Couplet under Iambic, n.

Example:


Taxonomy
iamb, iambs, stressed syllable, iambic, syllable, iambus, iambic trimeter, free encyclopedia, grid, horse, English, unstressed syllable, tree representation, iambic tetrameter, metrical tree, notation, iambic pentameter, Shall I compare thee to a summer's day.

Defination from the web:
iambus is a metrical foot used in various types of poetry. ... In ancient Greece iambus was mainly a satirical poem, a lampoon, which did not automatically imply a particular metrical type. ...