A-GPS (Assisted-Global Positioning System)

A  system that often significantly improves the startup performance—i.e., time-to-first-fix (TTFF)—of a GPS satellite-based positioning system. A-GPS is extensively used with GPS-capable cellular phones, as its development was accelerated by the U.S. FCC's 911 requirement to make cell phone location data available to emergency call dispatchers.

Ref:

NENA-STA-015, NENA Standard Data Formats for 9‑1‑1 Data Exchange & GIS Mapping