8:50 I can't find the dedicated knee video.

Great introduction! As long as we're disambiguating terms, I thought it was a step in the wrong direction to label "terminator" and "core shadow" as the same thing. The shadow terminator is where the surface "stops facing the light" (starting at 90 degrees). Everything beyond it is equally blocked and doesn't receive direct light. The effect is only that it's darker than the lit side. The terminator is relative to one light source. The core shadow is where the surface is receiving the least amount of both direct and bounce light. The effect is that some part of the shadow side is darker than others. But the core shadow moves if the bounce light moves, even if the primary light doesn't (and its shadow terminator doesn't). The core shadow is relative to the reflected light. Another way to think about it is that the core shadow is the shading effect of both the primary and bounce lights. As variation of the example in the video, if the table were diagonal, the bounce light would be stronger where the ball surface points towards the table. The core shadow would be on the side farther from the bounce light source. The source of the bounce light doesn't need to be so close for this to have an effect.