In photography, bokeh (Originally /ˈboʊkɛ/, /ˈboʊkeɪ/ boh-kay — also sometimes pronounced as /ˈboʊkə/ boh-kə, Japanese: [boke]) is the aesthetic quality of the blur produced in the out-of-focus parts of an image produced by a lens. Bokeh has been defined as “the way the lens renders out-of-focus points of light”. Differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye, while others produce blurring that is unpleasant or distracting—”good” and “bad” bokeh, respectively. Bokeh occurs for parts of the scene that lie outside the depth of field. Photographers sometimes deliberately use a shallow focus technique to create images with prominent out-of-focus regions.
The term comes from the Japanese word boke (暈け or ボケ), which means “blur” or “haze”, or boke-aji (ボケ味), the “blur quality”. The Japanese term boke is also used in the sense of a mental haze or senility. The term bokashi (暈かし) is related, meaning intentional blurring or gradation.
The English spelling bokeh was popularized in 1997 in Photo Techniques magazine, when Mike Johnston, the editor at the time, commissioned three papers on the topic for the March/April 1997 issue; he altered the spelling to suggest the correct pronunciation to English speakers, saying “it is properly pronounced with bo as in bone and ke as in Kenneth, with equal stress on either syllable”. The spellings bokeh and boke have both been in use since at least 1996, when Merklinger had suggested “or Bokeh if you prefer.” The term bokeh has appeared in photography books as early as 1998. It is sometimes pronounced /ˈboʊkə/ (boke-uh).
*** Definition and origin of bokeh courtesy of http://en.m.wikipedia.org/wiki/Bokeh ***