Iambic trimeter is a meter often found in Ancient Greek poetry. Each line consists of three iambs. An iamb is a two-syllable foot where the second syllable is emphasised, such as in the words 'today', 'amuse', or 'begin'. An example of a poem written in English in iambic trimeter is Emily Dickinson's The Only News I Know:
The only news I know
Is bulletins all day
From Immortality. [...]
The Inferno is the first volume of Dante's Divine Comedy (see bookmark to Page 33, "We'll be studying Dante, Virgil, all sorts of things." above) It is written in terza rima, an interlocking three-line rhyme scheme; Dante's is the first recorded use of this scheme.