please describe :
Density, specific gravity and viscosity.
Density is the ratio of mass to volume for a substance.
Specific gravity is density compared to density of water (For gases, it is often compared to the density of air).
Viscosity is the degree to which a liquid resists flowing. Water flows easily and has low viscosity. Oil is more viscous, grease is viscous to the point where you could debate whether it is a liquid or a soft solid (a lump retains its shape and doesn't slump). Viscosity is usually a strong function of temperature, for fats, oil, grease.
Google is a good tool to find more formal definitions for these terms.