What is Cross-platform
Building one codebase that ships as both an iPhone app and an Android app, using a framework like React Native or Flutter.
In plain terms
Cross-platform frameworks let a team reach both app stores from a single codebase. React Native builds on the same concepts as React for the web. Flutter is Google's framework and uses the Dart language. Expo is the common toolkit on top of React Native. The trade is some native polish for roughly half the engineering cost.
What it tells you about a developer
React Native skill signals a developer who can likely cover web frontend work too, since the React foundation is shared. That flexibility is valuable to a small team. Flutter skill is deep and self-contained. For a flagship app that needs native-level polish, Swift or Kotlin depth is the closer match, so confirm what the hiring manager actually needs.
Related
Read the lesson on Cross-platform More in Who does what on a team