JNA (Java Native Access) is a Java library for calling native shared libraries without writing JNI glue code. Instead of manually implementing native methods, developers declare `Library` interfaces or use `Native.register` direct mapping; the runtime proxies those calls through `NativeLibrary`, resolves symbols, and dispatches through a native JNI bridge backed by a vendored libffi copy. The core also supplies memory management (`Pointer`, `Memory`, `Structure`, `Union`), callbacks via native trampolines, string/array marshalling, custom type converters, and Windows stdcall/UNICODE mapping utilities.