"Promotion" is nothing to do with salary, seniority or status in this use case.
It means moving (promoting) software through different dev & testing stages and, finally, promotion into production. You can find this system in large IT team environments that develop and support integrated applications.
A common promotion sequence is Dev > QA testing > UA testing (user acceptance) > Production. If anything wrong is found by QA or UA it's checked back out of whatever stage it was at when the problem was found, back to the Dev environment. When the developer has fixed or modified it per discussion with the QA or UA tester, it's promoted again through the same sequence and re-tested along the way.
When called on to fix- or modify Production code, the code is "checked out" of Production back to Dev, and follows the same promotion sequence. Good QA- and UA testers are the developer's best friend. I always made a point of thanking them for testing my code, whether they found anything or not.