Keyword Research is the end-to-end process of finding, scoring and prioritizing the search terms an app should target, then placing each one in the metadata field where it can rank best.
Keyword research starts with a seed list: the words that describe what the app does and how its users talk about the problem. That list is expanded through store autocomplete, competitor listings, review language and Apple Ads (formerly Apple Search Ads), whose keyword tool shows popularity based on App Store searches; on Google Play, Play Console reports the search terms driving the most store listing visits. Each candidate is scored on popularity, difficulty and relevance, and the survivors go into the indexed fields, most valuable terms first — app name, subtitle and keyword field on the App Store; title, short description and full description on Google Play.
Research decides which searches an app can compete for at all, so mistakes compound: a term never placed usually isn't indexed, and a popular term the app can't credibly win spends scarce characters on nothing. Apple frames the core trade-off itself — popular terms may drive a lot of traffic but are highly competitive, while less common ones drive less traffic and are less competitive. Practitioners run research as a loop rather than a one-off: ship a keyword set with a release, read rank and conversion movement over the following weeks, retire what didn't move and test the next tier. Our App Store keyword research guide walks through each stage.
Example
A habit-tracking app seeds "habit", "streak" and "routine", expands them through autocomplete and its own reviews, and finds users keep writing "daily checklist". Scoring shows "habit tracker" is heavily contested while "daily checklist" is relevant and winnable, so the phrase goes in the subtitle and supporting words fill the keyword field.