Your answer
The error function is the function which you try to minimize. What you have listed above is a set of error functions, and the derivatives of some of them. It might be a bit confusing when litterature uses the same term when the minimizing function has been derivated. Just remember that we wish to minimize the error in our network, and the functions which helps us achieve it is the error function.
The error function
The most common error function is the the of the squares of the differences between all outputdesired and outputactual.