Term: Rhyme Scheme
A poem's rhyme scheme is the way its rhymes are arranged. Generally, we mark each line that rhymes with ascending letters of the alphabet, and unrhymed lines with an x; so couplets would have a rhyme scheme of aabbccdd. While this may seem obvious, it may be more useful when trying to describe a more complex stanza form, such as ottava rima, which has a rhyme scheme of abababcc. (Fred D'Aguiar's 'Bloodlines' is an example of this form.) Trying to describe the irregular distribution of rhymes in Charles Tomlinson's 'Jessica Learned to Kiss' is difficult in words, but it is easy to display as axa abbx ccdxdc xefxfe.