Relative Density (or Specific Gravity)
Ratio of the mass of a substance to the mass of an equal volume of a standard substance at a reference temperature. NOTE The standard substance is usually water; the reference temperature is usually 4 °C.
Source: API RP 10B-2, Recommended Practice for Testing Well Cements, First Edition, July 2005 (Reaffirmed: July 2010). Global Standards