Bokeh is a term from Japanese that means “blur” or “haze”. When using a lens with a shallow depth of field (e.g. you have it set to F1.8, as opposed to F22), light sources outside of your focus area can get hazy, and may appear as spheres of light. This could be a pleasing effect if intentional.

Here are some examples of pictures showing bokeh, and lack of bokeh.

The first shot shows a picture with a light source that’s out of focus. Since the shot was taken at a small aperture (F22), the light does not seem hazy. (Remember: an aperture with a high number, like F22, means a small opening).

Bokeh_1764Figure 1: No Bokeh

The second shot uses a large aperture (F1.8), so the out of focus light source looks more like globes of light.

Bokeh_1763Figure 2: Same light fixture, but with bokeh

For more on bokeh, check out this article in Wikipedia.