Why a thread on this subject? Because it's not been discussed enough. ;-)
OK, let's begin with Wikipedia:
https://en.wikipedia.org/wiki/Bokeh
In photography, bokeh (originally /ˈboʊkɛ/, /ˈboʊkeɪ/ BOH-kay — also sometimes pronounced as /ˈboʊkə/ BOH-kə, [boke]) is the aesthetic quality of the blur produced in the out-of-focus parts of an image produced by a lens. Bokeh has been defined as "the way the lens renders out-of-focus points of light". Differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye, while others produce blurring that is unpleasant or distracting—"good" and "bad" bokeh, respectively. Bokeh occurs for parts of the scene that lie outside the depth of field. Photographers sometimes deliberately use a shallow focus technique to create images with prominent out-of-focus regions.
Bokeh is often most visible around small background highlights, such as specular reflections and light sources, which is why it is often associated with such areas. However, bokeh is not limited to highlights; blur occurs in all out-of-focus regions of the image.
This is the definition I subscribe to. It is also the definition subscribed to on Rick Denny's excellent page on bokeh, chock full of examples:
http://www.rickdenney.com/bokeh_test.htm
Conversely, some wish to used the term "bokeh" to describe the amount of blur (as opposed to the quality of the blur) in the portions of the photo outside the DOF. I disagree with this usage of the term.
This semantic debate is *exactly* analogous to those who define exposure as the amount of light per area that falls on the sensor:
https://en.wikipedia.org/wiki/Exposure_(photography)
In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a photographic film or electronic image sensor, as determined by shutter speed, lens aperture and scene luminance. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.
and those who use the term to mean the brightness of the photo:
https://www.dpreview.com/articles/8148042898/exposure-vs-brightening
Does it matter? Well, inasmuch as words have meaning, yeah, it kind of does. But, if you're more of a "It means exactly what I want it to mean -- no more, no less" then, no, it really doesn't matter. Apologies if I forced you to have read this to the bitter end. ;-)
Of course, one might argue that a more pragmatic approach may be that one can infer the meaning from context. Sometimes, this is the case. but more often than not, it is not the case at all. For example, if someone asks, "What lens gives the most bokeh?", one can infer they want to get the most blur in the portions of the photo outside the DOF. But if one were to ask, "What lens has the best bokeh?", then the meaning is rather ambiguous if we accept that the term has two different meanings, just as is the case with the term "exposure".
Lastly, do I expect a resolution to the dilemma here? Of course not -- that would be silly. What I expect is that, just like the term "exposure", bokeh will continue to be used both correctly and incorrectly ( ;-) ) and the ambiguity will continue, which is unfortunate, since I think the distinction is important, inasmuch as any technical aspect of photography is important.
