To triangulate is to divide into triangles or use triangles to measure something. Sometimes people triangulate to measure distance. When you use three points to measure something, you triangulate.
Recognize the word triangle in triangulate? It’s no coincidence, both words come from the Latin triangulum for yes, “triangle.” When you triangulate, you make a series of triangles to measure distance or altitude. The height of a mountain and the distance to a river could both be estimated by triangulating. This type of triangulating is derived from trigonometry, which involves measuring the length and angles of triangles. You may have done that type of triangulating in math class.