In spectrophotometry, log of the ratio of the radiant power of the incident radiation to the radiant power of the transmitted radiation. SYN: absorbancy, absorbency, extinction (2), optic density.
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ab·sor·bance əb-'sȯr-bən(t)s, -'zȯr- n the ability of a solution or a layer of a substance to absorb radiation that is expressed mathematically as the negative common logarithm of the transmittance of the substance or solution called also optical density
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ab·sor·bance (ab-sorґbəns) 1. in analytical chemistry, the negative logarithm of the transmittance, −log10(I/I0), where I is the light intensity transmitted by the solution under analysis and I0 is the intensity transmitted by the pure solvent or other reference solution. Symbol A. Formerly referred to as absorbancy or optical density. 2. in radiation physics, the negative logarithm of the transmittance, defined as the ratio of the radiant energy transmitted by an object (I) to the incident radiant energy (I0).Medical dictionary. 2011.