You are right in some sense but IMO, sound money is a wealth backed by things with real value, wherein the thing that backs it won't lose value easily in this period and it does not go up and down in price rapidly. You can refer to gold and anything backed by it as a safe money, so long as it doesn't always decrease or increase in value. You can also say the same with other precious metals and anything backed by it(I might be wrong though since this is based purely from my opinion of it).