It seems that there are many confusion about this topic in the literature.
Some people takes nuclide as synonym of isotope. Other disagree. Also many resources discussing the difference define nuclide but then do not define isotope, but isotopes. I have tried to search the recommended IUPAC definition for isotope, but couldn't find it.
Therefore, this is my current understanding (please correct me if wrong):
Nuclide is an atom characterized by number of protons, number of neutrons and energy state.
Isotope is an atom characterized by number of protons and number of neutrons.
That is, isotope is a superclass of nuclide. Different nuclides (different energy states) are the same isotope. At the other hand we have the term isotopes.
Isotopes are a set of nuclides with equal proton number.
for example, carbon-12, carbon-13 and carbon-14 are three different isotopes of the element carbon. In its turn carbon-12 is an isotope, carbon-13 is another isotope, and carbon-14 is still another isotope.