Bokeh is a word you use to describe the effect of the blur or out of focus background that you get when shooting a subject. Simply put, bokeh is the pleasing or aesthetic quality of the out-of-focus blur in your photograph.
So, the bokeh “effect” is an extremely shallow depth of field. The difference between a shallow depth of field and bokeh is in the background of your image you will see circular shapes or hexagonal shapes. Now, what those shapes are, are beams of light traveling throw your lens and your aperture, hitting your light sensor. This is what creates those different shapes in the background.
It is usually achieved by using your widest aperture possible, such as f/2.8.
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