Complicated name aside, an isometric grid is your ticket to creating amazing 3D illustrations and designs.
An isometric illustration or design is achieved by a style of drawing which uses a technique called isometric projections. Through this technique, you can represent any 3D object on a 2D surface. Like your Mac screen.
Comparing true and isometric is a great way to understand what an isometric projection is. The angles of an isometric grid (and thus illustration or design) are infinitely parallel and never meet.