Whiles reading An Introduction To Statistical Learning under linear regression (Chapter 3), I found:
$$E(Y - \hat{Y})^2 = |f(X) - \hat{f}(X)|^2 + Var(ε)$$
where $E(Y - \hat{Y})^2$ represents the average, or expected value of the squared difference between the predicted and actual value of $Y$, and $Var(ε)$ represents the variance associated with the error term $ε$.
What does $Var(ε)$ mean? Can we just write $ε$ rather than $Var(ε)$?
