Time To First Fix (TTFF) is a measure of the time required for a GPS receiver to acquire satellite signals and navigation data, and calculate a position solution (called a fix).
The TTFF is commonly broken down into three more specific scenarios, as defined in the GPS equipment guide:
Many receivers can use as many as twelve channels simultaneously, allowing quicker fixes. Many cell phones reduce the time to first fix by using assisted GPS (aGPS): they acquire almanac and ephemeris data over a fast network connection from the cell phone operator rather than over the slow radio connection from the satellites.