Compositing is an optimizational workflow for minimizing render iterations while maximizing your render output's editability. It's essentially the concept of separating your render into individual components that can be reconstructed and tweaked independently after rendering.

Compositing is sort of like Apple TV in that it's very useful but can be difficult to explain and understand. So let's break it down into a problem -> solution explanation.

The Problem -----------------
Rendering is always the bottle neck of a production pipeline due to the extended time required to render animation. So when we commit to a render, wait hours or days for it to finish, only to decide after the fact that we want ??the? [metallic material] to reflect 50% less, our only choice is to make that change in the shader then render and wait again. This is where compositing comes in.

The Solution -----------------
Someone had the brilliant idea to separate rendered elements - like objects, material color, reflections, lighting, etc - so they could be tweaked individually after rendering. Now to continue with the previous example, we could reduce reflections by 50% with the compositor in 5 seconds instead of waiting hours to render the whole scene again.
That's the meat and potatoes of compositing. And in this course we're going to explore how we can disasseMble and reasseMble a 3D render with Blender's Node Editor.