A choir or choral group is a collection of people who sing together. They typically rehearse together with a leader and perform concerts or sing during religious services. Some choirs are professional (the singers are paid for their work in the choir). Some choirs are semi-professional (the leaders are paid at a professional rate for their work with the choir but the singers are not). Some choirs are amateur or recreational (the leaders are either not paid or are offered an honorarium and the singers are not paid). Some amateur choirs invite anyone who is interested sing with them. Professional, semi-professional, and some amateur or recreational choirs require interested people to audition and then select their members based on a set of audition criteria. 