In any given Congress there may be as many as 12,000 House bills introduced - and serval thousand Senate bills
Only 250 to 800 of those bills actually make it through to become a Public Law. So most bills die in committee.
Public Laws are laws passed during a particular session of Congress. They are also called "session laws" A few may be new legislation, but most are amendments to existing law. SEE THE TAB ON FEDERAL SESSION LAWS
Public Laws are then incorporated into the complilation of existing federal law called the U.S. Code.
