Explain Correspondence limit or Correspondence principle?
Correspondence limit (N. Bohr): The limit at which a more common theory decreases to a more specialized theory when the situations that the specialized theory needs are taken away.
Correspondence principle (N. Bohr): The principle that whenever a new, more common theory is put forth, it should diminish to the more specialized (and generally simpler) theory under normal situation. There are correspondence principles for the general relativity to special relativity and special relativity to Newtonian mechanics, however the most widely termed correspondence principle (and usually what is meant when one states "correspondence principle") is that of quantum mechanics to the classical mechanics.