The Bedford Glossary of Critical and Literary Terms - Ross Murfin 2018
Rhyme scheme
Rhyme scheme: The pattern of rhyme in a poem or stanza, typically described by assigning a lowercase letter to each new rhyming sound. Certain poetic forms, such as the sonnet, triolet, and villanelle — as well as stanza types, such as the Spenserian stanza — are conventionally composed in accordance with a specific rhyme scheme. Thus the rhyme scheme of a ballad stanza is abcb, whereas that of an Italian sonnet is generally abbaabbacdecde.