Bokeh is the aesthetic quality of the out-of-focus areas in a photograph or video frame, referring specifically to the visual character of the blur rather than simply the presence of blur itself. The term comes from the Japanese word for blur or haze and describes how points of light and background detail render when they fall outside the lens's depth of field, with different lenses producing distinctly different bokeh characteristics.

The quality of bokeh is shaped primarily by the optical design of the lens, including the number and shape of aperture blades, the focal length, and the lens's minimum focus distance. Lenses with many rounded aperture blades produce circular, smooth bokeh discs from point light sources - often considered the most aesthetically pleasing. Lenses with fewer straight aperture blades produce polygonal bokeh shapes. Some vintage lens designs produce swirly or turbulent bokeh that has become sought after for its distinctive quality. Faster lenses at wide apertures produce more pronounced bokeh because the shallower depth of field leaves more of the image outside the focus plane. In portrait and subject photography, attractive bokeh in the background separates the subject from its environment, creating a sense of visual depth and isolation that draws attention to what is sharp.

AI image and video generation models have a strong understanding of bokeh as a visual quality because it appears consistently throughout their training data. Descriptions like "shallow depth of field with soft circular bokeh," "creamy background blur," "subject isolated against smooth bokeh," or "fast prime lens bokeh quality" communicate this optical characteristic effectively and tend to produce generated imagery with the distinctive depth separation and background quality of wide-aperture lens photography.