Adjustment layer: A special kind of layer that holds information about the changes made to the associated layer rather than the entire layer’s information.
Adobe Camera Raw (ACR): Used to convert RAW files into files that Photoshop can open.
Ambient light: The general background light in a given situation.
Aperture: The size of the opening in a camera lens.
Blending mode: Determines how two layers in Photoshop will combine.
Bracketing: Shooting many exposures at a range of settings. It is more common to bracket shutter speed than aperture.
Burn: To selectively darken an area in an image.
Channel: In Photoshop, a channel is a grayscale representation of color (or black) information. In RGB color there are three channels, red, green, ...