In photography, bokeh 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”. Bokeh is very important in many types of photography, but especially in portraiture, wildlife and macro photography. The soft background focus allows the viewer to focus better on the subject at hand. Some lenses produce better Bokeh than others.
Bokeh is controlled by the aperture settings. Depth of field knowledge is essential in obtaining the right results, especially since a larger aperture is required to obtain good results. Larger apertures reduce depth of field and a too-shallow depth of field may not have the entire subject in focus. There is a careful balance that must be managed, otherwise, focus stacking will be required. You can see in the example below that the out of focus background is very soft and allows the viewer to focus on the sharp subject. The Bokeh in this example compliments the image with minimal distraction.
Also see: Aperture and Depth of Field.