Final answer:
The slope of the security market line represents the Beta coefficient, which measures the systematic risk of a stock compared to the market.
Step-by-step explanation:
The slope of the security market line represents the Beta coefficient in financial terms.
Beta coefficient is a measure of the sensitivity of a stock's returns to the overall market returns. It measures the systematic risk of a stock compared to the market. A higher Beta coefficient indicates higher volatility and greater risk, while a lower Beta coefficient indicates lower volatility and lower risk.
Therefore, the correct answer is D) Beta coefficient.