The President’s Cabinet is made up of a few people that are considered his most trusted advisors: the Vice President and the heads of the 15 federal executive departments. The major function of this body is to advise the President on any matter relating to their respective executive departments, as established in Article II, Section 2, of the U.S. Constitution:
"The President (...) when called into the actual service of the United States; he may require the opinion, in writing, of the principal officer in each of the executive departments, upon any subject relating to the duties of their respective offices ... "