Edge enhancement is a black or white outline that is
added to foreground objects, such as someone's head, so that it stands
out from the background. This is an artefact that is not present in the
original source material, and is added in to make a transfer look better
when viewed via a poor quality medium, such as VHS tape. Edge enhancement
is not necessary on DVD because of its inherently much higher resolution
and only serves to create an annoying halo around objects. It can be confused
with back-lighting. See here
for a fabulous, in-depth discussion of edge enhancement.
American Pie 33:10
Note the whitened left edges of these images. When blown up to
a reasonable size on a display device, these lines change from being an
enhancement to the clarity of the image to being a distraction.