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Iambic: adjective - characterized by, or based on iambuses, of a poet using iambic metres: noun - an iambic foot or poem, a metrical unit with unstressed-stressed syllables.
This term is used to describe a classical type of verse, in which a short syllable is followed by a long one, unaccented. Shakespeare is usually considered to have written in iambic pentameter, though not all his lines follow the rule when spoken in a natural voice. But, I can do no better here than quote the undisputed master.
And Gentlemen in England now abed
Shall think themselves accursed they were not here,
And hold their manhood cheap, whiles any speaks
That fought with us upon Saint Crispin's day.
(Shakespeare, Henry V, act IV, scene III)