Expected Return is a forward-looking financial metric representing the probability-weighted average of all possible future returns. In portfolio optimization, it is typically estimated using historical averages, macroeconomic factor models, or analyst forecasts.
It is a core input in Modern Portfolio Theory (MPT) and Mean-Variance Optimization. By knowing the anticipated return and volatility (risk) of various assets, one can calculate the most efficient allocation of capital.
Keep in mind that the Expected Return is merely an average of thousands of potential outcomes. In any single given year, the actual return of a volatile asset will almost certainly differ—sometimes significantly—from its Expected Return.