Triangular coordinates
The term triangular coordinates may refer to any of at least three related systems of coordinates in the Euclidean plane:

 a special case of barycentric coordinates for a triangle, in which case it is known as a ternary plot or areal coordinates, among other names
 Trilinear coordinates, in which the coordinates of a point in a triangle are its relative distances from the three sides
 Synergetics coordinates

Triangle geometry
Coordinate systems