Bokeh - If your starting out with photography and manual lenses, you will probably come a cross that word. The word comes from ”boke”, the Japanese word for blur. It is used to describe the part of a picture that are out of focus, and that the lens shows as blurred. Bokeh of lenses may have very different aesthetic qualities. This is most apperent in larger apertures, when part of the picture is a lot out of focus. Soft edges on the blurry reflexes are often considered preferable!
Bokeh of Helios 44-3
Some great reading about bokeh:
Great Bokeh-test from Rick Denney
Ken Rockwell on bokeh
Understanding bokeh by Merklinger