A term borrowed from the Japanese, pronounced with short vowels. (ie: more like French pronunciation - bo-ké - versus long English diphthongs - bow-kay.) Essentially bokeh, which is derived from the Japanese for blurring, refers to the highly subjective quality of the out of focus areas of a picture. Good bokeh is generally held to be smooth and soft, whereas bad bokeh is generally held to be distracting in some way - perhaps clumpy or doubled-up bright spots and so on.

Bokeh can be important for portraiture - you want out of focus areas behind the subject to be smooth and as non-distracting as possible. Highly patterned or sharp-edged areas don’t look as good. Mirror lenses are notorious for bad bokeh - they have annular (ring or doughnut shaped) out of focus highlights.

Bokeh is also written without the H, but the H is usually added to remind English speakers that the word has two syllables and not one.