Absorbance

The absorbance (also optical density, or OD) of a material or suspension is a measurement of the amount light it absorbs at a particular wavelength. Absorbance is abbreviated with a capital 'A' (or OD) followed by the wavelength in nanometers, for example, A280 is the absorbance at 280 Nanometer|nm. A higher OD260 (optical density at 260 nm light) means a sample absorbs more light at that wavelength.

Use in Biochemistry
In biochemistry, the absorbance at 600 Nanometer|nm (OD600) is used to measure the concentration of bacteria in a sample.