OpenGL - Simple definition of clipping?

Question

From my understanding clipping is the process of differentiating what is on the screen and what shapes lie outside of the screen and providing measures to give priority to what 'primitives' the user should see.

Also I may be digressing but is this a primitive?

{x,y,z} - (a vector or matrix of points)

Answer 1

Clipping is explained in detail here and also here. Basically points are clipped if they are outside of the frustum defined by the projection matrix.

I do not see what you mean with "primitives", but OpenGL generally uses homogeneous coordinates, thus a 4D vector (x,y,z,w). w is 1 initially but may be different after projection. See also this article for more info about homogeneous coordinates.