The Beer-Lambert Law describes the relationship between the concentration of a solute in a solution and the amount of light absorbed by that solution. It states that the absorbance of light is directly proportional to the concentration of the solute and the path length of the light through the solution. This principle is commonly used in chemistry to determine the concentration of substances in various solutions. In practical applications, the Beer-Lambert Law is utilized in fields like spectrophotometry, where instruments measure how much light is absorbed at specific wavelengths. By knowing the absorbance and the path length, one can calculate the concentration of the solute, making it a valuable tool in laboratories and industries.