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Bokeh refers specifically to the aesthetic quality of the blur produced in the out-of-focus parts of an image—especially the smooth, creamy, or pleasing blur in backgrounds when using a fast lens (e.g., f/1.4). It is not simply "blur," but the character of the blur.
The keyword is built on a common misspelling, but the correct term— boke —has a rich, fascinating history. Originating from classical Japanese verbs for senility ( bokeru ) and blurriness, it evolved into the cornerstone of Japanese comedy, a mild affectionate insult, and a globally recognized photography concept.