self-taught
Mach-O (Mach object) file format, is a file format for executables, object code, shared libraries, dynamically loaded code, and core dumps. It was developed to replace the a.out format.
Mach-O is used by some systems based on the Mach kernel. NeXTSTEP, MacOS, and iOS are examples of systems that use this format for native executables, libraries and object code.