Delta is not an error but what does it mean when scanning for artifacts and it changes from saying Delta of 0 in 0 pixels to saying there are Deltas in pixels? Artifacts usually follow, so Delta's seem like a precursor to errors/artifacts.
Delta means difference, it's a common word mostly used in mathematics and statistics. Delta underlines the fact that the frames produced by your card are different from the reference frames. In this case, delta is the amount of incorrect pixels.
"delta 0 in 0" will be reworded to no errors or no artifacts in the next version
delta xx in yy means: yy pixels do not match the reference .. the total amount of error (how much the pixels are wrong in color compared to the reference) is xx