Triangulation

Full definition of triangulation

(countable and uncountable; plural triangulations)

(uncountable) A technique in surveying in which distances and directions are estimated from an accurately measured baseline and the principles of trigonometry
(countable) The network of triangles, so obtained, that are the basis of a map or chart
(uncountable) In navigation or seismology, a process by which an unknown location is found using three known distances from known locations.
(chess) A delaying move in which the king moves in a triangular path in order to force the advance of a pawn.
(qualitative research) The use of three (or more) researchers to interview the same people or to evaluate the same evidence to reduce the impact of individual bias.

2003, Nahid Golafshani, Understanding Reliability and Validity in Qualitative Research (in The Qualitative Report Volume 8 Number 4 December 2003 597-607) http://www.nova.edu/ssss/QR/QR8-4/golafshani.pdfTriangulation was established by asking researcher #2 and researcher #4 to conduct their own interview of the participant.