Abnormal return refers to the portion of stock returns not attributable to the market or the sector as a whole.

It is calculated by taking the difference between the actual return and the expected return based on general market conditions. For example, if the return on a fund is 25% and the market as a whole has increased by 17%, then there is an 8% abnormal return.

This term is often used in financial analysis to evaluate whether an investment strategy or manager is outperforming expectations given the level of risk and market conditions.