Selective Availability

Overview
Selective Availability (SA) was an intentional degradation of public GPS signals implemented for national security reasons. In May 2000, at the direction of President Bill Clinton, the U.S government discontinued its use of Selective Availability in order to make GPS more responsive to civil and commercial users worldwide. The United States has no intent to ever use Selective Availability again.

In September 2007, the U.S. government announced its decision to procure the future generation of GPS satellites, known as GPS III, without the SA feature. Doing this made the policy decision of 2000 permanent and eliminated a source of uncertainty in GPS performance that had been of concern to civil GPS users worldwide.

Source

 * GPS.gov (full-text)