As I've discussed in the past on this blog, the photography term "bokeh" refers to an out-of-focus area of an image. A photo is often considered to have "good bokeh" if those areas have a smooth, silky look, or are generally pleasing to the eye.
I could describe the many ways that the word "bokeh" is pronounced, but that's a whole other discussion that I'd rather not get in to.
I could also discuss the many ways that good bokeh is achieved. But I don't want to make this an instructional post. I'm also no expert on the subject. I just know the way I do it.
It all has to do with depth-of-field - i.e. the in-focus depth of the image. Therefore lens and aperture choice have something to do with it, as does your distance to the subject, since they all affect depth-of-field.
The other day I decided to take advantage of a nice day and grab some images in my backyard. I used my telephoto lens (my favorite), and I was able to frame some shots in such a way as to generate some nice green background...backyard...bokeh.
Here's the best three shots of the day. (In the first two images, the green background is actually just the grass in my backyard.)
Good bokeh makes for a good background, and good backgrounds are necessary for good photos.
That's pretty good - somebody oughta put that on a coffee mug or something.