Y-intercept of a regression line

In $\hat{y} = a + bx$ (read y-hat for $\hat{y}$), the y-intercept $a$ is where the line crosses the vertical axis, which is the predicted response at $x = 0$. Technology computes it alongside the slope, and you interpret it in context whenever $x = 0$ is a realistic value. For example, if $\hat{y} = 84 + 3.2x$ predicts adult height in centimeters from foot length in centimeters, the intercept claims a person with a foot length of 0 cm stands 84 cm tall, which is nonsense, while $x = 25$ gives the sensible $84 + 3.2(25) = 164$ cm. Report the intercept as part of the equation, and say plainly when $x = 0$ sits far outside the observed x-values.