General computing term.
IBM: "Native memory is the memory provided to the application process by the operating system. The memory is used for heap storage and other purposes."
Geode: "The available native memory on a machine is the difference between the machine's physical RAM and the memory used by the processes running on it. It is actually even less than that since the operating system also uses some of this memory."
.NET Memory Profiler: "Native memory is the memory managed by the operating system, rather than the Common Language Runtime."