Abnormal return refers to the portion of the return on shares that cannot be attributed 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 risen by 17%, then there is an 8% abnormal return.

This concept is often used in financial analyses to evaluate whether an investment strategy or manager is performing better than expected, given the level of risk and market conditions.