The angle of effective coverage for sound radiated from a speaker. When looking at speaker specifications, you'll see this listed with two components, horizontal and vertical (i.e. 90 degrees x 60 degrees).
“My Sales Engineer has always been really knowledgeable; he's right there with all the information I need. I've been very happy dealing with Sweetwater in general - there haven't been any negatives.” Ted Kynard, Charlotte, NC