Φ (Phi): The diameter of the opening used to screw filters onto the end of a lens.
Adobe Camera Raw (ACR): Used to convert RAW image files into files that Photoshop and other software can open.
Aperture: The size of the opening in a camera lens, usually designated as an f-stop.
Blending mode: Determines how the pixels in two layers in Photoshop will combine.
Bokeh: Out-of-focus blurring.
Bracketing: Shooting many exposures at a range of settings. It often works better to bracket shutter speed rather 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 the RGB color space there are three channels, red, green, and blue.