When annotating a poem, each letter corresponds to a (n)

When annotating poetry, each letter corresponds to a separate rhyme scheme. For instance, in the poem Twinkle Twinkle little star how I wonder what you are Up above the world so high Like a diamond in the sky the first two lines would be marked with one letter, lets use A, and the second two lines would be marked with a new letter, lets use B. Part A is a rhyme because star and are rhyme while part B is a new rhyme using high and sky.