What does MEDIN mean on your W-2

Where?  In box 14?  You have to ask your employer.  They can put anything in box 14.  Med probably means medical.

I assume the MEDIN is in box 14. There are no rules or standards for the information in box 14, or for any abbreviations that are used. The employer can put pretty much whatever they want in that box. My guess is that MEDIN stands for medical insurance, but if you want to know for sure, you have to ask your employer what it means.