Conversion Funnel is the path a user takes from seeing your app to installing it — impression, to product-page view, to download — where each step has its own drop-off to diagnose and fix.
The ASO funnel has three measurable stages: an impression (your app appeared in a result or list), a product-page view (someone tapped through), and an install. Each transition is a separate conversion rate with a separate cause. The impression-to-tap step is won by your icon and first screenshots; the tap-to-install step is won by the full gallery, ratings, description, and any app preview video. Looking at one overall number hides which step is actually leaking.
Diagnosing the funnel tells you where to spend effort. If you get plenty of impressions but few taps, the problem is your icon or first screenshots, not your gallery. If lots of people view the page but don't install, the issue is further down — weak proof, low ratings, or a confusing value proposition. Optimizing the right stage is the difference between a fix that moves installs and a redesign that changes nothing.
Example
An app with strong impressions but a low tap-through rate redesigns just its icon and first screenshot — the top of the funnel — and lifts installs without touching the rest of the listing.