macOS has a lot of lingo… So based on my research on the topic, macOS is a platform which contains a GUI much like Gnome for Linux (called Aqua in the graphic)
but the actual OS is called Darwin, which is open source
and their entire kernel is called XNU which is also all open source
XNU is made up of 2 main components: BSD and Mach
Mach was a microkernel and BSD is BSD… They took parts of both and combined them into one
and that created their XNU kernel
Apparently you can call “Core OS” functions which are much like ntdll.dll on Windows or the native API
but people rarely do that anymore… Mostly its using managed Cocoa which uses Swift or Objective-C
much like C# on Windows
ALso I noted that processes on Mac are called Tasks instead
and what Windows called HANDLEs are called Ports on Mac
so a thread can have ports