What is Capital Asset Pricing Model?

Legal Definition
In finance, the capital asset pricing model (CAPM) is a model used to determine a theoretically appropriate required rates of return of an asset, to make decisions about adding assets to a well-diversified portfolio.
-- Wikipedia
Legal Definition
In finance, the capital asset pricing model (CAPM) is used to determine a theoretically appropriate required rate of return of an asset, if that asset is to be added to an already well-diversified portfolio, given that asset's non-diversifiable risk. The model takes into account the asset's sensitivity to non-diversifiable risk (also known as systematic risk or market risk), often represented by the quantity beta in the financial industry, as well as the expected return of the market and the expected return of a theoretical risk-free asset.