What is 'Apple MFI Certified'?

Without knowing what the "product" is: Identify counterfeit or uncertified Lightning connector accessories - Apple Support provides an explanation.

That designation is used to let the consumer know that the charging cable has been certified by Apple. However, I have no way of knowing if the product you're looking at is "legitimate" or not. I expect that scammers might lie about something like MFI certification status.