Choral (kɔ́rəl) music is, simply put, music written for a musical group of singers to perform. Choir size can vary, depending on the size of the written piece of music. A group can be as small as twelve, or as large as a thousand. Music such as this has been around since the early Medieval times, and is still popular today. In the Medieval period, a form of choral music that was very popular is called a Rondeau, which is a strict pattern of repetition of both refrain and verse that follows the scheme of a poetic form. One of the most influential composers of this musical period is Johannes Ockeghem.