Photography: the aesthetic quality of the blur produced in the out-of-focus parts of an image captured by a lens.
Etymology: from the Japanese word boke (暈け or ボケ), which means “blur” or “haze”, or boke-aji (ボケ味), the “blur quality”. Boke is also used in the sense of a mental haze or senility. The term bokashi (暈かし) is related, meaning intentional blurring or gradation. Content Source.