App Store Search Algorithm is the system that ranks apps for a search query based on keyword relevance in metadata combined with performance signals like downloads, conversion, and ratings.
App store search ranking rests on two pillars. The first is relevance: does the app's metadata — title, subtitle, keyword field on the App Store; title and description on Google Play — contain the queried terms, and how prominently? The second is authority: how does the app perform, measured by download velocity for that term, tap-through and conversion rates, retention, and ratings? An app can be relevant but rank poorly because it converts badly, or perform well overall but miss a keyword entirely.
This two-pillar model is why ASO can't be only a metadata exercise. You can edit your way to relevance, but authority is earned through real user behavior. The practical loop is: add the keyword to be eligible, then improve conversion and ratings so the algorithm trusts you enough to rank you above competitors who also use the term.
Example
Two apps both put "meal planner" in their metadata, but the one with a higher conversion rate and more recent download velocity for that term ranks above the one that merely mentions it.