In simple terms, it refers to the excess returns a scheme generates over and above the returns its benchmark index (for e.g., the Nifty) has generated.
Positive Alpha indicates a performance better than the benchmark index, while negative alpha indicates underperformance.
Alpha = % Returns from the fund – % Returns from the benchmark index
For example if fund return is 10% while Nifty Index returned around 8% in the same time, then alpha would be 2%