I sent this article to my programmer hubby to explain for me in exchange for 'favors'. He sent me back an email so full of acronyms and buzzwords that I am going to meet him at the door tonite with a pancake on my head.
Then around 1990 the owners of UNIX published a specification for an executable format called "Executable and Linkable Format" (ELF) and most UNIX vendors adopted it. Most executables for UNIX are created in this format because it's a free and open format -- most UNIXes can understand it, and anybody can write it.
SCO, having bought the UNIX business, claims that ELF is proprietary information, that IBM ripped them off by "putting it into Linux," but unfortunately for them it's a freely published interoperability standard that has been in wide use for over a decade.