Difference between static and shared libraries in Android's NDK?

The term shared library is not a perfect fit regarding Android's NDK, because in many cases the .so libraries aren't actually shared between applications. It's better to classify the libraries that the NDK builds as static and dynamic.

Every Android application is a Java application, and the only entry point for the NDK code is loading it as a dynamic library and call it trough JNI.

Static libraries are an archives of compiled object files. They get bundled in other libraries at build time. Unused portions of code from static libraries are stripped by the NDK to reduce total size.

Dynamic libraries are loaded at runtime from separate files. They can contain static libraries that they are dependent on or load more dynamic libraries.

So what you actually need for Android development is at least one shared library, that will be called from Java code, and linked with it's dependencies as static libraries preferably.

Native shared libraries: The NDK builds these libraries, or .so files, from your native source code. Native static libraries: The NDK can also build static libraries, or .a files, which you can link against other libraries.

This is according to NDK Documentation