Case's pocket sharpener, and stones to hold an angle on
Inclusive angle is the whole angle between the two sides of a knife's edge, as opposed to the angle on one side alone. Case's Mini Pocket Sharpener page uses the term with two numbers in one sentence: "The 40 degree inclusive angle maintains a consistent 20 degree double edge on most knives." Böker USA says knife and sharpener makers state the angle either way.
On its Mini Pocket Sharpener page, Case gives 40 degrees as the sharpener's "inclusive angle" and 20 degrees as the "double edge" it maintains "on most knives." Böker USA names both conventions in its post on sharpness: an angle given as "an absolute angle between the two sides of the blade," with 40° as its example, or as half of it, the angle between the grinding material and the center of the blade, with 20° as its example. The two sides being measured are the edge's bevels, and an inclusive figure takes in both.
Among the makers' own angle lines, Buck's how-to page is the one that writes "per side." Case's knowledge-base article, Kershaw's FAQ, Gerber's how-to and Böker USA's steel guide each print a figure without saying whether it covers one side or both, so a bare 20 degrees on one of those pages could follow either convention, and Böker's own example uses 20 for the half. Each maker's figures, in the maker's words, are collected on what angle knife makers sharpen at. Where a page leaves it open, ask the maker directly or check the paperwork that came with the knife; converting the figure yourself is a guess.