Singing is an art form in both public and private schools. Karaoke, for example, can be a fun hobby and a kind of casual entertainment. A record label may hire a professional singer and pay for the production and recording of their work. Other companies, such as radio advertising corporations and variety show theaters, may hire singers. Professional singers who perform on cruise ships are known as cruise ship singers. Some cruise ship singers will sign a contract with a single cruise line and act only on that line’s ships, but others may sign multiple agreements with different cruise lines.