Brian C. Miller , Mar 11, 2003; 09:23 a.m.
This is supposedly a Japanese word which refers to the areas of a picture which are out of focus. (At the moment I can't find the word in an online Japanese-English dictionary, but boke and bokke produced this, and a wild card search produced out of focus)
This aspect of the lens produces things like out-of-focus highlights being either round or pentagonal, depending on aperture blades, in-lens reflection due to various coatings, etc.
I wouldn't rely on "bokeh" to make or break a picture, though.