Jaggies

A slang term, maybe, but 'jaggies' refers to jagged diagonal lines that appear in a low resolution image. Pixels are square, so if large pixels are being used to represent a diagonal, you'll be able to see the corners of each, creating a saw-like edge. Anti-aliasing is used to soften jaggies, whereby the software will attempt to calculate 'in-between' shades to blur the line a little and make it look smoother.