When you buy an asset you become exposed to a bundle of different risks. Many of these risks are not unique to the asset you own but reflect broader possibilities, such as that the stock market average will rise or fall, that interest rates will be cut or increased, or that the growth rate will change in an entire economy or industry. Residual risk, also known as alpha, is what is left after you take out all the other shared risk exposures. Exposure to this risk can be reduced by diversification. Contrast with systematic risk.