A rhyme scheme is found in poetry (and in songs). It is a pattern of rhyme that is used, with similar sounds found at the end of lines grouped together.
[A rhyme scheme is] the pattern of end rhymes or lines. A rhyme scheme gives the scheme of the rhyme; a regular pattern of rhyming words in a poem (the end words).
The rhyme found at the end of lines can be seen in the following example from Shakespeare's Sonnet 29:
For thy sweet love remembered such wealth brings
That then I scorn to change my state with kings.
Sounds are assigned letters. One sound is assigned an A; when a new sound at the end of a line is introduced, it is given a B. If a sound is repeated in two subsequent lines at the start of the poem, the duplicated sounds are shown as AA.
In a poem where the first and third lines rhyme and the second and fourth lines rhyme, it is "charted" as ABAB, also as seen in Sonnet 29:
When in disgrace with Fortune and men's eyes,
I all alone beweep my outcast state,
And trouble deaf heaven with my bootless cries,
And look upon myself and curse my fate,
"Eyes" and "cries" rhyme, and "state" and "fate" rhyme—they have the same sound. This is a popular rhyme scheme—charted, as mentioned, as ABAB.
Another popular rhyme scheme is seen with ABCB. Refer to the stanza (four-line section) below from Samuel Taylor Coleridge's epic (long) poem The Rime of the Ancient Mariner:
The ice was here, the ice was there,
The ice was all around:
It cracked and growled, and roared and howled,
Like noises in a swound! (58-61)
With this example, "there" (A) and "howled" (C) do not rhyme (and are given different letters to reflect the different sounds), but "around" (B) and "swound" (B) do rhyme, and the rhyming pattern of this stanza is written as ABCB.
Poetry is very much like music. A variety of literary devices can create a musical quality in a poem. One of these devices is found in the end rhyme of a group of lines, where a pattern of rhyme has been followed by the author. This is the rhyme scheme—the rhyming pattern that the author uses in writing his poem.
A rhyme scheme is a regular pattern of rhyme, one that is consistent throughout the extent of the poem. Poems that rhyme without any regular pattern can be called rhyming poems, but only those poems with an unvarying pattern to their rhymes can be said to have a rhyme scheme.
Rhyme schemes are labeled according to their rhyme sounds. Every rhyme sound is given its own letter of the alphabet to distinguish it from the other rhyme sounds that may appear in the poem. For example, the first rhyme sound of a poem is designated as a. Every time that rhyme sound appears in the poem, no matter where it is found, it is called a. The second rhyme sound to appear in the poem is designated b. Every other time that rhyme sound appears in the poem, no matter where it is found, it is called b. The third rhyme sound to appear would be c, the fourth d, and so on, for as many rhyme sounds as appear in the poem.
The following short poem illustrates the labeling of a rhyme scheme.
There once was a big brown cat a
That liked to eat a lot of mice. b
He got all round and fat a
Because they tasted so nice. b