Dwell time

Borrowed from search engine optimisation, where it sits between two observable events: the click, and the return to the results page. A quick bounce back suggests the page did not answer the question. A long stay suggests it did. Google has never confirmed dwell time as a direct ranking factor, and no public tool measures it, which makes it a good way to think and a poor thing to chase. The nearest figure you can actually see is average time on page, and that has no idea where the visitor went next.