Taken from Wikipedia
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”
Using the effect of Bokeh when shooting was first introduced to me when I was fairly new to photography. I generally will shoot wide open to accentuate my subject with a creamy backdrop or frame. It is especially useful when you find a subject that has an interest to you and it is surrounded by boring areas. When these areas have a light source, be it a bulb or reflection of natural light it can be quite magical.