Bokeh

From the Japanese word for blur. Bokeh describes the quality of what is defocused: the shape of specular highlights, and how busy or calm the background reads. Round, smooth highlights look pleasant, while harsh onion-ring or cat's-eye shapes pull the eye away from the subject. Aperture blade count and lens design do most of that work, which is why some lenses are prized for their bokeh and others are cheap for a reason. The usual slip is using the word to mean the amount of background blur. That is depth of field, controlled by aperture, focal length and distance. Bokeh is what the resulting blur looks like.