Originally Posted by vasantn
I believe this is a myth (as far as the origin of FO is concerned), and that the term FO (the internal DL code for Silver Medallion) was originally an acronym for "Flies Often".
Thanks to Mikey likes it for asking a question that's been in the back of my mind for a while. And thanks to vasantn for the answer. My guesses were way off. I assumed it referred to the low level Medallion benefits such as
First
On (the aircraft) or
Firstclass
Occasionally.