What is a cartesian coordinate?

Answer 1

That should be plural: "Cartesian coordinates". That's the most common type of coordinate system, with coordinates that are usually at right angles to one another - for example (x, y), or (x, y, z).

Answer 2

For Cartesian coordinates in n-dimensional space there are n axes which are [usually] orthogonal and which meet at a single point called the origin. The coordinates of any point in the n-space are defined by ordered n-tuples whose terms refer to the distances of the point, from the origin, along each of the axes.