Machobject

Mach Object Format

Mach-O, short for Mach object file format, is a file format for executables, object code, shared libraries, dynamically-loaded code, and core dumps. A replacement for the a.out format, Mach-O offered more extensibility and faster access to information in the symbol table. It's most notably the object format used on Mac OS X.

See the Wikipedia article for more information.