Wireless Assisted GPS (WAG or waGPS)

Generally uses advanced chipsets capable of acquiring very weak GPS signals and integrating the signals very quickly to determine location. WAG distributes GPS functionality between a 1) GPS reference receiver, 2) Location Server, 3) and GPS-enabled client device. The Reference Receiver provides GPS data and precise time to the Location Server. The Location Server computes and provides aiding data to the client, and performs navigation solution upon receipt of GPS measurements from client. The client pre-processes and returns basic GPS measurements along with statistical measures that characterize the signal environment.

Source: http://www.w3.org/

*Bonus WotD: TV-GPS uses synchronization signals from television stations to determine handset location when indoors. Because of the frequency and power of TV signals, they often can be received at indoor locations where GPS signal cannot.