The pattern of end rhymes in a poem is called "rhyme scheme". It refers to the way in which the end sounds of lines of a poem are organized or repeated. Rhyme scheme is often denoted by assigning a different letter of the alphabet to each new rhyme, with matching sounds given the same letter. For example, a poem with the rhyme scheme ABAB has the first and third lines ending in words that rhyme with each other, and the second and fourth lines ending in words that rhyme with each other, creating a pattern. The rhyme scheme of a poem can help to create a sense of unity and structure, and it can also help to create a particular mood or tone.