A coordinate in a Cartesian coordinate system. In 2 dimensional space, the coordinates are commonly designated by (x, y) or (x₁, x₂). In three- dimensional space, they are commonly designated by (x,y,z), (χ, η, ζ), (x₁, x₃, x_x) or (x₁, x_. , x₃). The last of these is the most usual if tensors are being used.