Tap-Through Rate (TTR) is the share of people who, after seeing your app in search or browse results, tap through to open its product page — the App Store's version of click-through rate.
Tap-through rate measures the very first conversion in the funnel: of everyone who saw your app as a search result or chart entry, how many cared enough to tap. At that moment the only things a user can judge are your icon, your app name, and — in search results — your first one or two screenshots. A high TTR means those few assets are winning the glance against everything else on the screen.
TTR matters beyond the tap itself because it's a relevance signal. When lots of people who see your app for a query choose to open it, the algorithm reads that as evidence you belong there and tends to hold or lift your rank. A weak TTR quietly caps everything downstream: it doesn't matter how good your product page is if too few people ever reach it.
Example
Two habit-tracker apps rank side by side for the same term; the one with a cleaner icon and a benefit-led first screenshot earns more taps, and over a few weeks its stronger TTR helps it edge ahead in rank.