Definition of ordinary differential equation

Is a differential equation ordinary if it only contains derivatives with respect to one variable, even if the function has multiple variables?

For example the function y=f(x,t) and the differential equation
$\frac{d^2y}{dx^2}+2\frac{dy}{dx}=4$ would that be ordinary are partial?

Does the question not make sense because if you already know how many (independent) variables the function (in this case $y$) depends on, then it wouldn't be a differential equation because the function isn't unknown?