External validity is related to generalizing.
That's the major thing you need to keep in mind. Recall that validity refers to the approximate truth of propositions, inferences, or conclusions. So, external validity refers to the approximate truth of conclusions the involve generalizations . Put in more pedestrian terms, external validity is the degree to which the conclusions in your study would hold for other persons in other places and at other times. In science there are two major approaches to how we provide evidence for a generalization.