A repetition poem is a poem that repeats a syllable, accent, sound, etc. It can be a word, a sentence, or a phrase. It is a poetic device that creates expectation and rhythm.
Repetiton is used to re-inforce a theme or idea in most poems. However, u have to look at the poem u are studying specifically to see the real effect of repetition
A line, or part of a line, that repeats later in the poem is called a refrain. Poetic forms that make use of a refrain include rondeaus, triolets and villanelles.