Bokeh (pronounced 'bo' as in bone, and 'keh' as as in kelly) comes from the Japanese word boke which means blur or haze or the blur quality.
[via Wikipedia] "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" or "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. Bokeh is often most visible around small background highlights, such as specular reflections and light sources, which is why it is often associated with such areas. However, bokeh is not limited to highlights, as blur occurs in all out-of-focus regions of the image."
Here are eight wonderful examples of creative bokeh photography. Be sure to click on the link after the images to see even more!
40 Beautiful Examples of Bokeh Photography @ thephotoargus.com