A hymn is a religious song of praise to God or a god. Hymns have been sung since ancient times and in various religions and regions, including Egypt, Israel, Greece and the Indian subcontinent. Traditional hymns in Christian services are typically formal songs that are based on classical music and that often contain biblical references. They are usually sung in unison by the entire congregation in public worship and are often accompanied by an organ in traditional services and by electric guitars and a drum kit in more contemporary services.