Well, I don't know what it means in this case (common usage), but I can tell you what it means in layman-engineering terms. Take Rockvirgo's email, the part about the wave being reflected back negatively. If the power amp has a feedback loop, it'll see that reflection, and try to correct for it. The feedback loop is fast -- but not instantaneous. Depending on the signal, the reflection, and the speed of the feedback loop, the amp will just never get the output right. First it'll try to push the power in one direction, overshoot and go back the other way. If things get really bad (you get some resonance) the amp can diverge wildly from the intended signal. But, if you have a reasonably talented person designing the amp and feedback loop, this won't happen -- at least at audible frequencies. Maybe this is why rumor has it that high bandwidth amps can be more prone to this effect? It's been a long time since I've done any engineer stuff -- looking back is a bit fuzzy.... Perhaps someone else can improve on this explanation.
Can speaker cables damage amplifiers?
I have been told on good authority that network cables such as TRANSPARENT and MIT can cause broad bandwith amplifiers (eg Krell) to "go into oscillation" and thereby cause some nasty damage. These cable manufacturers, apparently, are aware of this problem. Can anyone confirm this?