A teacher (also called a school teacher or, in some contexts, an educator) is a person who helps others to acquire knowledge, competences or values.

Informally the role of teacher may be taken on by anyone (e.g. when showing a colleague how to perform a specific task). In some countries, teaching young people of school age may be carried out in an informal setting, such as within the family, (homeschooling) rather than in a formal setting such as a school or college. Some other professions may involve a significant amount of teaching (e.g. youth worker, pastor).