In the regression equation Y = a + b X, a is called:

The correct answer is: B. Y-intercept

The Y-intercept is the point where the line crosses the Y-axis. In the equation $Y = a + bX$, the Y-intercept is the value of $Y$ when $X = 0$. Therefore, the Y-intercept is $a$.

The X-intercept is the point where the line crosses the X-axis. In the equation $Y = a + bX$, the X-intercept is the value of $X$ when $Y = 0$. Therefore, the X-intercept is not given by the equation $Y = a + bX$.

The dependent variable is the variable that is being predicted by the independent variable. In the equation $Y = a + bX$, $Y$ is the dependent variable and $X$ is the independent variable.

Therefore, the correct answer is: B. Y-intercept