Market Return
The Market Return is commonly used in the CAPM formula to calculate the Cost of Equity (CoE). It is typically quantified as the average return for a major market index like the S&P 500. It is used in conjunction with Beta to determine the Market Risk Premium.
In the room
One of two inputs to the market risk premium. Being able to name a reasonable figure and its source — long-run S&P 500 average — keeps you from freezing on a follow-up question.