Final answer:
A poem's end rhyme pattern, designated by assigning lowercase letters to each new rhyme, is called a rhyme scheme, such as ABAB or ABABCC, and is used to create a musical quality that can support the poem's mood and themes.
Step-by-step explanation:
The pattern of end rhymes used in a poem and denoted by assigning each new sound a lowercase letter of the alphabet is known as a rhyme scheme. This is an analytical method used to describe the pattern of rhyme within a stanza or throughout a poem. For example, if the first and third lines rhyme and the second and fourth lines rhyme, this is denoted as ABAB. If another sound is introduced in the fifth line that rhymes with the second and fourth, the scheme would continue as ABABC, and so on with each new rhyme sound being represented by the next letter in the alphabet.
In the given example of a poem's stanza with the rhyme scheme ABABCC, there is a clear pattern where the first and third lines rhyme, as do the second, fourth, and sixth, with the fifth and sixth lines sharing a different rhyme. This rhyme scheme contributes to the musical quality of the poem, makes the text memorable, and often supports the poem's mood and themes.