App Store Optimization (ASO) is the practice of improving an app's visibility and conversion in app store search and browse so it earns more organic installs without paying per download.
App Store Optimization works on two fronts at once. The first is visibility: getting the app to surface for the searches and browse surfaces real users see, which is driven mostly by the keywords in your metadata and your historical performance. The second is conversion: turning the people who see your listing into installs, which is driven by your icon, screenshots, ratings, and the first line of your description. A keyword strategy that ranks but doesn't convert wastes the impression; a beautiful listing nobody finds wastes the design. ASO is the discipline of doing both together.
Because roughly two-thirds of App Store downloads start with a search, ASO is the highest-leverage organic channel most apps have — and unlike paid acquisition, the gains compound. A ranking you earn this month keeps delivering installs next month at no extra cost. The mechanics differ between the App Store and Google Play, but the goal is identical on both: be findable for the right intent, then be the obvious choice once found.
Example
An app that adds "habit tracker" to its subtitle and redesigns its first two screenshots might rank for a new high-intent term and lift its conversion rate at the same time — two ASO levers, one update.