Many people (including myself) use the word "triangulation" very loosely here
because it's a word most people can understand, but purists would not call what
GPS does "triangulation" because no angles are involved. But just so we don't
confuse new folks learning GPS, it's really "trilateration" or "resection".

Ref: http://www.trimble.com/gps/triangulation.html
http://www.Colorado.EDU/geography/gc...gps/gps_f.html

Trilateration
The measurement of distances... to fixed positions to determine an
originating location. The process is normally to control points on the
surface of the earth. In GPS trilateration, the fixed positions are
instead satellites orbiting the earth with distance determined by the
GPS signal travel time to a location on the surface of the earth. A
four satellite trilateration provides an accurate earth position.


Triangulation
The measurement of angels... to determining the location of an unknown
point, as in GPS navigation, by using the laws of plane trigonometry.