Along with DOF you will often see the word bokeh used. Again, just like DOF it will be used in such a way that the writer is assuming you know what it means. Essentially it is the non-focussed bit, the blurred bit of photographs outside the depth of field area. The best person to explain it is the photographer who has had most to do with bringing it to popular use in the west, Mike Johnston:
It’s a Japanese term, written with two characters in Kanji, previously romanized as “bo-ke” or boke … I changed the spelling of the romanized word to “bokeh.” It’s properly pronounced in two syllables, equally stressed, with “bo” as in bone and “ke” as in Kenneth—quite similiar to “bouquet,” actually, except that the last sound is more of a an eh and not so much an ay.
The Japanese word means, roughly, “blur,” and, actually, I often say “blur” now instead of bokeh. As a photographic term it simply refers to the blur of objects out of the depth of field.
Source: The Online Photographer: Bokeh—What It Is 
There is an excellent technical article on the subject here by Paul van Walree with great demo photographs to explain everything.
Coming as I do from computing and marketing backgrounds I get easily irritated by people using “technical” terms when there are perfectly adequate normal English words that can be substituted. This is why I tend to say “blurred bit” rather than bokeh or boke. If you want a bit of fun, point people using the phrase to the linked post above and let them know they are spelling it wrong.
Technorati Tags: photography, term, boke, bokeh, dof, dslr
