Usage is a value that describes a number of certain actions taken against a feature, or the product as a whole, that do not represent the actual usefulness of either. Because you have sixteen thousand clicks on a button means nothing for how much value it provided to the user – for all we know, the user might’ve been frustrated enough where he or she clicked a couple of times and quit the app. As an example, think of it as a way to correlate time spent in the product, feature usage, number of returns to the product in a day and conversion rate (read: user achieving a goal established in the product).