Channel
From The Glossary of Digital Photography
(1) One of the three colors (red, green, or blue) that make up a color image. (2) A grayscale image made up of the information from only one of the color channels. In Photoshop, with an image open, by opening the channel mixer (Window>Channels) and clicking on each channel individually, the photographer can see the three grayscale images with each one based on a different color channel. Opening each grayscale image, the photographer can see the differences in the information stored in each channel. If working with just a grayscale image, there will be only one channel. An RGB image will have three channels, a CMYK image will have four. See also RGB; CMYK; gray scale
