Evaluation of Multilateration technology as a possible replacement for the E-scan PRM at Detroit (DTW) was initiated, as required by Congressional language. The MLAT subsystem, known as PRM-A, will provide accurate position and identification Information on transponder equipped aircraft and surface vehicles by "mulblaterating" on signals transmitted by the transponder.
Source: wiktionary
Among these new techniques, MLAT (Multilateration) is one of the most representative and typical. MLAT locates a target by accurately computing the TDOA (time difference of arrival) of a signal emitted from the target to three or more receivers, and it has attracted the world by its potential to achive high accuracy and update rate.
Source: wiktionary
The WAM system provides surveillance in the en route airspace while MLAT is used to ensure surveillance of the terminal area airspace or ground traffic at the airport.
Source: wiktionary