Relative return is a measure of the return or profit of an investment portfolio relative to a theoretical passive reference portfolio or benchmark.[1]
In active portfolio management, the aim is to maximize the relative return (often subject to a risk constraint). In passive portfolio management, the aim is to obtain a relative return as close to zero as possible, thereby reproducing the return of the theoretical reference portfolio. When the relative return is positive, the portfolio is said to outperform the benchmark. Conversely, when the relative return is negative, the portfolio is said to underperform the benchmark.
Within passive portfolio management, the absolute value of the relative return is often called the tracking error, which is confusing since the tracking error is more generally defined as the standard deviation of the relative return. Index funds are the financial products that use passively managed portfolios.