Market equity beta measures the covariability of a firm's returns with all shares traded on the market (in excess of the risk-free interest rate).
We refer to the degree of covariability as systematic risk. The market prices securities so that the expected returns should compensate the investor for the systematic risk of a particular stock. Stocks carrying a market equity beta of 1.20 should generate a higher return than stocks carrying a market equity beta of 0.90. Nonsystematic risk is any source of risk that does not affect the covariability of a firm's returns with the market. Some writers refer to nonsystematic risk as firm-specific risk. Why is the characterization of nonsystematic risk as firm-specific risk a misnomer?