Obviously, pilots trained in different places see these definitions in the opposite sense to each other!
This should not be too surprising when one considers that many countries don't even agree about which side of the road to drive on!
Perhaps the best way to resolve the issue is to avoid using the "side" or "forward" slip terminology altogether whenever possible. Slip to control drift while maintaining alignment or slip to add drag for a steeper descent. Call it whatever you wish or call it nothing at all!
This is all pretty amusing isn't it?