Absorbance is a measure of how much light is absorbed by a substance when light passes through it. It is commonly used in fields like chemistry and biology to analyze the concentration of a solution. The higher the absorbance, the less light is transmitted through the sample, indicating that more light has been absorbed by the molecules in the solution. Absorbance is often measured using a spectrophotometer, which shines light of a specific wavelength through the sample. The absorbance value is calculated using the formula A = log10(I0/I), where A is absorbance, I0 is the intensity of the incident light, and I is the intensity of the transmitted light.