The legislative branch of the American federal government consists of two houses, the Senate and the House of Representatives, which are jointly known as Congress. Sessions of both houses are held in the Capitol Building in Washington D.C. The Capitol is situated on Capitol Hill, and in common parlance, "Capitol Hill" is often used a shorthand for Congress itself.
The powers of Congress are set out in Article 1 of the U.S. Constitution. The relative powers of the three branches are not defined in the Constitution, but the Supreme Court under Chief Justice John Marshall asserted its power to interpret the Constitution and declare legislation unconstitutional if necessary. This power is called Judicial Review.
Congress exercises certain powers over the other branches through its control of the impeachment process. Federal officials, including members of both the judicial and executive branches, can be impeached, i.e. charged, by the House of Representatives. A trial resulting from impeachment is conducted in the Senate.