Channel

Let's imagine you're looking at a page from a coloring book. Now, imagine three versions of this page - one where you have only colored the red parts, another where you have only colored the green parts, and a third where you have only colored the blue parts.

Each of these versions is like a "channel" in a picture that a computer looks at. So, a picture or image has different channels, usually red, green, and blue, that together make up the whole picture.

In depth reference can be found here