The Cartesian coordinate specifies every point uniquely in a plane using numerical coordinates using the numerical coordinates which are singed distances from the point to 2 perpendicular lines (axis) called x and y . In the case of 3 dimensional objects or points another axis called z can be added perpendicular to y to point out points in a 3 dimensional space.
This video shown below explains extensively about the 3 axis and 2 axis coordinate systems.
3D Geomteric Modeling
3D Geometric modelling is used by all 3D applications when making 3D objects. This could include simple geomtric objects such as lines, curves and arcs to 3D objects such as cubes, spheres and such. This is also the center of everything to to with computer generated 3 dimensional objects, from video games to movies. All objects 3D objects created in a virtual 3D plane requires geometry to exist.
(http://www.webreference.com/3d/cararra/images/fig1_12.jpg)
