Noun: Exemption from penalties, payments or legal requirements, granted by authorities or statutes. Generally there are four types of immunity at law: 1) a promise not to prosecute for a crime in exchange for information or testimony in a criminal matter. 2) Protection of public officials  from liability for their decisions. 3) Governmental immunity which protects government agencies from lawsuits unless the government agreed to be sued; 4) Diplomatic immunity which excuses foreign ambassadors from most U.S. criminal laws.