SD is the standard deviation (also known as the margin of error) above/below the DRC+ value assigned to each hitter.
We report standard deviation to recognize that there is uncertainty around any metric that attempts to define a player's mathematically expected contribution. Uncertainty is useful when comparing players: if two players of differing DRC+ values have overlapping ranges of plus/minus deviation around their respective values, then it could be agued that they made comparable contributions. If the two players do not overlap, even when the plus/minus deviation is added to their DRC+ values, then we can be fairly confident that one contributed more than the other.
dAVG, dOBP, dSLG, and dOPS are the revised results-based statistics based on the number of singles, doubles, walks, etc. that DRC+ has awarded. These numbers are usually less than the raw numbers, although not always. *The 'd' stats* are not intended as a representation of value, but are included to provide insight into DRC+.