An exequatur is a legal document issued by a sovereign authority allowing a right to be enforced in the authority's domain of competence. The word is a form of the Latin verb exequi, and means let it be executed in Latin.
An exequatur is a patent which a head of state issues to a foreign consul, guaranteeing the consul's rights and privileges of office and ensuring recognition in the state to which the consul is appointed to exercise such powers. If a consul is not appointed by commission, the consul receives no exequatur; the government will usually provide some other means to recognize the consul. The exequatur may be withdrawn, but in practice, where a consul is obnoxious, an opportunity is afforded to his government to recall him.
Roman Catholic Canon Law
An exequatur is a legal instrument issued by secular authorities in Roman Catholic nations to ensure that Papal teachings have legal force within their jurisdiction. The tradition began during the time of the Western Schism, when the legitimately elected Pope gave secular leaders permission to verify the authenticity of papal decrees before enforcing them.
Some dissidents in the church claim however that the tradition arose because of the state's inherent power of the church and that such state privilege in reviewing Papal teachings was exercised since the early days of the church. However, official church teaching denies that any permission from secular officials is necessary for Papal pronouncements to be legally effective, though local officials sometimes fail to enforce the law. 
In Mexican, Spanish, French and Italian law, an exequatur is a judgment by which a tribunal (In the case of Italy, the Court of Appeal) states that a decision issued by a foreign tribunal should be executed in their corresponding jurisdictions.