aliasing and anti-aliasing

Aliasing is a Web design term used to describe the undesirable distortion of visual elements on a computer screen. These peculiarities take many forms, such as the appearance of jagged or stair-stepped edges along what is supposed to be a smooth, curvy surface (like an O or S) or diagonal lines on the screen (also known as "the jaggies"). Anti-aliasing is a software technique used in imaging systems (such as Photoshop) to make these curved edges or diagonal lines look smooth and continuous.