Side weight is the imbalance between the left and right side of the grip center line after drilling. Per USBC standards, it can be no more than 1 oz. There is also an imbalance of 1 oz allowed between the finger hole side and the thumb hole side as measured from the center of the grip. The allowed imbalance between the top of the ball and the bottom is 3 oz to allow for the differences in weight removed from drilling.
PS this should probably be posted in another forum like the Misc or Drilling and Layouts. It will not show up on the front page drawing better informed replies. If you are wanting to know how to find this weight, you would get a better answer in the Drilling And Layouts forum.