*Photography Glossary
Bokeh A buzzword used to describe the aesthetic qualities of the out-of-focus parts of an image, with some lenses producing "good" bokeh and others offering "bad" bokeh. Boke is a Japanese word for "blur," and the h was added to keep English speakers from rhyming it with broke.
Out-of-focus points of light become disks, called the circle of confusion.
Some lenses produce a uniformly illuminated disc.
Others, most notably mirror or catadioptic lenses, produce a disk that has a bright edge and a dark center, producing a "doughnut " effect, which is the worst from a bokeh standpoint. Lenses that generate a bright center that fades to a darker edge are favored, because their bokeh allows the circle of confusion to blend more smoothly with the surrounding. The bokeh characteristics of a lens are most important when you are using selective focus (say, when shooting a portrait) to deemphasize the background , or when shallow depth-of -field is a given because you're working with a macro lens, long telephoto, or with a wide-open aperture. See also mirror lens, circle of confusion.
Blur In photography, to soften an image or part of an image by throwing it out of focus, or by allowing it to become soft due to subject or camera motion. In image editing, blurring is the softening of an area by reducing the contrast between pixels that form the edges.
*Referance DIGITAL SLR PHOTOGRAPHY David D. Bushch