A substitute teacher is a person who teaches a school class when the regular teacher is unavailable (e.g., because of illness, personal leave, or other reasons. While "substitute teacher" is the generally use phrase in the United States and Canada, supply teacher is the more common term in the United Kingdom and Ireland (though the term is also used in Canada), and relief teacher is used in Australia and New Zealand. An "emergency teacher" or a "sub" is another name for a substitute teacher in Australia. There are also various other terms which may be used in a particular region (such as teacher on call T.O.C. in the Canadian province of British Columbia).