A measure of selection risk (also known as residual risk) of a mutual fund in relation to the market. A positive alpha is the extra return awarded to the investor for taking a risk, instead of accepting the market return. For example, an alpha of 0.4 means the fund outperformed the market-based return estimate by 0.4%. -0.6 means a fund's monthly return was 0.6% less than would have been predicted from the change in the market alone.
In a Jensen Index, it is factor to represent the portfolio's performance that diverges from its beta, representing a measure of the manager's performance.