"Bokeh" is how English-speaking photographers spell the Japanese word that in Hepburn romanization is spelled boke, so that you don't think it's just one syllable, like "broke" without the "r". The Japanese word means "blur" or "haze" (not just visual--it's used to refer to mental fuzziness as well), and photographers use it to refer to what lenses do with things not in focus. Bokeh can be used to good effect--it can keep your eye on the subject, which is in focus, and it can make for a pleasant (if you're lucky) or unpleasant (if you're not--for real lenses it depends on how the lens is built and the shape of the aperture) background.
I was making sure I knew what I was talking about (that the current official SL client makes it easy to turn on snadows) and found that the client had been set such that the depth of field was shallow--and the result was some pretty nice bokeh. I had to take a picture, and here it is:
Now to learn how to control it (and find out whether or when it will be in Firestorm!).