Why SAR stands for Specific Absorption Rate, the quantity used in RF safety work to describe how fast RF energy is deposited in body tissue. It is expressed in watts per kilogram of tissue, and FCC exposure limits for devices used close to the body (handhelds, for example) are stated as SAR limits rather than as field strength or power density. Power density in mW/cm^2 is used for far-field exposure evaluation, while SAR covers the near field where the body is within a fraction of a wavelength of the antenna.
Watch out The choices about signal attenuation or amplification just borrow the initials S and A; SAR has nothing to do with gain or loss in a circuit, and nothing to do with terrain reflection.
SAR = Specific Absorption Rate, watts per kilogram absorbed by tissue. Think 'absorption', not 'amplification'.