In computing, something is referred to as native when it is designed to run on a particular platform.
The platform is usually an operating system or a processor but it could also be a device. If software runs on a computer natively, it means that it runs without any external layers. For example, to run software native to Windows on macOS, an emulator is necessary. It is a layer that makes one computer system behave like another computer system. But software native to macOS doesn’t need an emulator layer to run on a Mac.
Native code is code that is written for a certain processor. This phrase is mostly applicable when talking about differences in CPUs. In general, native code is machine code – a low-level numerical programming language used to directly control the CPU. Developers mainly write code in higher-level languages and this code is then compiled into machine code. Since CPUs differ, the machine code differs. That is why the phrase “native code” is used when wanting to emphasise the differences.