Smoothing the jagged appearance of diagonal lines in a bitmapped image. The pixels that surround the edges of the line are changed to varying shades of gray or color in order to blend the sharp edge into the background. This technique is also called "dithering," but is usually known as anti-aliasing when applied to diagonal and curved lines.
Smoothing a distorted signal by applying various techniques that add data or filter out unwanted noise.
This teapot from the University of Utah was a famous first example of anti-aliasing applied to images. (Images courtesy of Computer Sciences Department, University of Utah.)