NOUN (2)

1. a trigonometric method of determining the position of a fixed point from the angles to it from two fixed points a known distance apart; useful in navigation;

2. a method of surveying; the area is divided into triangles and the length of one side and its angles with the other two are measured, then the lengths of the other sides can be calculated;

The Collaborative International Dictionary of English v.0.48:

Triangulation \Tri*an`gu*la"tion\, n. [Cf. F. triangulation.]
   (Surv.)
   The series or network of triangles into which the face of a
   country, or any portion of it, is divided in a
   trigonometrical survey; the operation of measuring the
   elements necessary to determine the triangles into which the
   country to be surveyed is supposed to be divided, and thus to
   fix the positions and distances of the several points
   connected by them.
   [1913 Webster]

WordNet (r) 3.0 (2006):

triangulation
    n 1: a trigonometric method of determining the position of a
         fixed point from the angles to it from two fixed points a
         known distance apart; useful in navigation
    2: a method of surveying; the area is divided into triangles and
       the length of one side and its angles with the other two are
       measured, then the lengths of the other sides can be
       calculated

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "triangulation":
   appraisal, appraisement, approximation, assessment, assize,
   assizement, automatic tracking, calculation, computation,
   correction, data transmission, determination, estimate, estimation,
   evaluation, flector tuning, gauging, instrumentation, locking on,
   locking signals, mapping, measure, measurement, measuring,
   mensuration, metric system, phase adjustment, pinpointing,
   precision focusing, quantification, quantization, radar navigation,
   radar-telephone relay, range finding, rating, scan conversion,
   scanning, signal modulation, survey, surveying, telemetering,
   telemetry, three-pointing, tracking, triggering signals,
   valuation