The USA Patriot Act is a counter-terrorism act that was enacted in October, 2001, and reauthorized in 2006. The title is actually an acronym (Uniting and Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism).
The Patriot Act is hugely expansive in its text as well as its scope. Below are two links: (1) The full text of the Act; and (2) a section-by-section analysis conducted by U.S. Senator Patrick Leahy of Vermont.