Answer: Market risk premium.

The security market line (SML) is a graphical representation of the capital asset pricing model (CAPM), where the x-axis represents systematic risk (beta) and the y-axis represents expected return. The slope of the SML is the **market risk premium**, which reflects the additional return investors require for taking on market risk. - **Option A** is incorrect because the security's beta is the slope of the security characteristic line (SCL), not the SML. The SCL plots the excess return of the security against the excess return of the market. - **Option C** is incorrect because the slope of the capital market line (CML) is the market risk premium divided by the market standard deviation, not the SML.

Author: LeetQuiz Editorial Team