Definitions for "Abnormal returns"
The excess of returns over the level of return that would be expected given the riskiness of a portfolio.... more on: Abnormal returns
The component of the return that is not due to systematic influences (market-wide influences). In other words, abnormal returns are above those predicted by the market movement alone. Related: excess returns.
The component of the return that is not due to systematic influences (market-wide influences). In other words, the abnormal returns is the difference between the actual return and that is expected to result from market movements (normal return). Related: excess returns. Source