Bokeh

You know those blurred light dots in an image? That's the Bokeh. "The way the lens renders out of focus points of light". It is easy to adjust and play around with these parts of the image in a creative way. You can change the shape of the bokeh by creating a make shift lens cap with a custom shape cut out from it. This post goes into detail about how to and pics of others. Here are some cool ideas I've seen..