The Expo framework gives you the module system, runtime environment, CLI tools, debugger, a suite of modules, navigation to build universal native apps. They're universal in that there is an Android build, an iOS build, and a web build, and, especially with Expo Router, they work together with universal links. They're native in that the user experience is native to the underlying platform, usually using system UI components and behaviors.
EAS provides hosted services for building your app, submitting it to the stores, and updating it. Many developers will use both EAS and their own hardware. It is convenient and fast to build locally when iterating on a feature. And it is convenient in a different way to use EAS to make preview builds of your app on your PRs that change your app's native code or to make release candidates for production.