Channels, Layers, and Shaders

Channels hold layers stacks, filled with paint layers, procedurals, and adjustments in your project. For example, a project might have channels for diffuse color, displacement, or specularity, but each of those channels contain individual layers for paint, masks, and filters. Channels can then be used in shader inputs so you can adjust the amount of diffuse or specularity, among other things.

Video:  Watch Understanding Shaders and Channels for a brief overview about Channels.