A constitutional monarchy is a form of monarchy in which the sovereign exercises authority in accordance with a written or unwritten constitution.Constitutional monarchy differs from absolute monarchy (in which a monarch holds absolute power) in that constitutional monarchs are bound to exercise their powers and authorities within the limits prescribed within an established legal framework. For example, the power of the sovereign (King or Queen) was greatly limited in Britain after signing the English Bill of Rights

edited from: https://en.wikipedia.org/wiki/Constitutional_monarchy