online gallery: Internet sharing services that allow you to post your images to the Web.

opacity: The degree to which a layer allows layers beneath it to show through.

optical viewfinder: A glass-covered opening in your camera that you can look through to frame and compose your image.

optical zoom: A traditional zoom lens; has the effect of bringing the subject closer and shortening depth of field.

overexposed: When too much light hits the camera’s film or image-sensor array, resulting in a washed-out image.