It stands for degrees per side. As it sounds like you already know, an edge bevel that is 15 DPS could also be described as having a 30 degree inclusive angle. An edge that's 18 degrees on one side and 12 degrees on the other could be described as having a 30 degree inclusive angle as well. I pretty much assume if someone says 26 degrees inclusive, they mean 13 DPS, unless they say otherwise.
The other big set of edge characteristics are the asymmetry of the edge bevels. A perfect edge with 15 DPS and exactly the same size bevel that meet to a point in the middle of a blade would be a perfect "V" with 50/50 asymmetry. If you keep the same angle on each side and grind a bevel that's about a 2-to-1 size ratio with the right side bevel being the larger, that's roughly a 70/30 right hand asymmetry on the edge. The point of the now asymmetrical "V" will be moved towards the left side of the blade. You can extrapolate the rest for left hand biased asymmetry or higher ratios, etc.
As I understand it, people create edge bevels with right or left hand biased asymmetry to either create higher performing edges, or help a blade exhibit neutral steering characteristics through taller product, given a particular blade grind geometry.
OK, I need a soda break now...