In the United States, the Executive branch consists of the Office of the President, including certain members of the United States Cabinet and the Presidential Staff, as well as a large number of federal agencies. The Executive branch in the United States is limited by the separation of powers with the Legislative branch and the Judicial branch.
Compare this system of checks and balances with the system in the United Kingdom. There, the executive is the British monarch, who is essentially a figurehead whose power is restricted by convention and public opinion. The Prime Minister, generally regarded as being the real authority in the UK, is himself or herself a member of Parliament, which is the legislature.