pixel
The smallest square of colour in a raster (bitmap) image.
resolution
The amount of detail in an image, often given as width × height in pixels; for printing, pixels per inch (ppi).
raster image
An image made of pixels, such as a photo or digital painting.
vector image
An image made from mathematical points, lines and curves; it can be enlarged without losing sharpness.
layer
A separate transparent level in a digital image that can be edited on its own.
non-destructive editing
Editing in a way that keeps the original (adjustment layers, duplicates, masks) so changes can be undone later.
exposure
How much light a photo captures; too much is overexposed (washed out), too little is underexposed (too dark).
frame rate
In animation or video, the number of frames (still images) shown per second (fps).
lossy compression
Making a file smaller by discarding some image data, as JPEG does; repeated saving lowers quality.