or "jagged edges", or "jaggies"

Aliased versus Anti-Aliased Edges
Ever noticed a tiny white rim around the edge of an irregularly shaped image that was placed on a dark background? Chances are the designer had anti-aliased edges on the image, then tried to use a transparency feature (such as transparent GIFs or transparency in Director) to show the image on a different color background. Anti-aliasing is a way that the computer smooths rounded edges to make them appear less choppy from the low resolution of a computer screen. When the image is made transparent, you are allowed to choose only one specific color to be removed. To eliminate a white background and see another color beneath it, a transparency feature may remove all white pixels. But it will hide only pixels that are exactly white. Anti-aliasing blurs edges to smooth them out, which means there are pixels that are nearly white but are shades of the edge of your image. These light pixels will not be made transparent, so they show up harshly on a dark background. To have a clean transparency, disable any features that will anti-alias the edges of your image. Note that this affects only images that are irregular in shape because the computer displays images in a rectangle. Graphics that are already rectangular have no need for transparency (unless you want an area within the borders to be made transparent).
http://podgoretsky.com/ftp/Docs/Internet/Creating ShockWave ...

Jaggies, bitmapped, aliased
Aliasing is the description given to jagged edges on curves and diagonal lines in bitmap images. They can be more easily seen if the image is enlarged to above 100% of its size.

Aliasing is unavoidable to some degree with on-screen images because of the fact that computer screens use pixels that run horizontally and vertically. In printed images, the jaggies can be avoided by using a digital image with a high enough resolution.

Anti-aliasing is the process whereby the jagged 'aliased' edges of a bitmapped image, or on-screen font, are smoothed.
http://www.designtalkboard.com/glossary/design/a-glossary.ph...

Anti-aliasing is a process that attempts to minimize the appearance of aliased or jagged diagonal edges, or “jaggies.”
http://www.spec.org/gwpg/publish/fsaa_in_vp10.html