Abnormal returns is a term used by stock market traders to describe the difference between a single stock or portfolio's performance in regard to the average market performance (usually a broad index s.a. the S&P 500 and EURO STOXX 50 or a national index like the Nikkei) over a set period of time. For example if a stock increased by 5%, but the average market only increased by 3%, then the abnormal return was 2% (5% - 3% = 2%). If the market average performs better than the individual stock then the abnormal return will be negative.

In contrast, excess returns are returns above the risk-free rate, as used in the CAPM.