For some reason, this old question has been completely changed in the last few weeks to something that makes both of the existing answers entirely wrong. Why? One of the edits says "to clarify the intent of the original poster", but how can one know the intent of the original poster?
The question was completely changed from "What is meant by Vf?" to something about Chinese power tools that have "Vf" marked on them, without any indication that the original asker was talking about power tools. This revision was made on January 26 of 2021, more than six years after the question was posted and subsequently closed on September 29 of 2014.