What is meant by S.M.V?

The S.M.V. (Sake Meter Value) measures the density of sake relative to water, and this is the barometer for gauging the dryness or sweetness of the sake. The higher the S.M.V., the drier the sake The median value of S.M.V. is +3. However, even different brands with the same S.M.V may be perceived as being drier or sweeter.
Often times one might think that the S.M.V. has a great deal of variance from sake to sake tasted, when, in fact, it does not. The variation may be due to the variations in the sugar or level of acidity. The S.M.V. is only intended as a reference number to give you a rough idea of how dry or sweet the sake is likely to be.