build
The process that turns your project files into an app you can run or ship.
Like baking a cake from ingredients, a build takes your source files and produces an app you can run or ship.
Builds matter because they catch errors, freeze versions, and create the files the stores expect. For Android that work happens in Android Studio or through Expo's build service.
In practice, you run a build for testing and another for release. The release build is signed, marked as coming from you, and is the one you upload.