Bokeh

Bokeh is the use of depth of field so that different parts of the photo in focus. Typically, foreground is sharp and background is blurry. Changing aperture (f stop) on the camera allows you to make a large aperture (low number, e.g. 2.5) which gives you more bokeh or vice versa. In this shot, the center bird is sharply in focus and the farther back you go, the less sharp/more blurry the birds become. In this photo, Bird Bokah, depth can be conveyed by relative sizes (the farther birds appear smaller) and by selective focus (bokeh). Some photographers use Lens Babies to artificially create bokeh, but I prefer to not manipulate bokeh.