The study of rhythm in music is similar to the study of rhythm in poetry. Songs are poems set to music. Metre is a term covering both the underlying rhythm and the structure on top of the rhythm. The repeated rhythmic unit from which a poem is is constructed is called a Foot. It is a pattern of long and short syllables. These syllables correspond to strong and weak beats in a bar of music. There is one difference - it matters where a rhythmic pattern begins in poetry but does not matter where the rhythmic pattern begins in music.