Throughout my career I think that the two most misunderstood functions within a telephone system are Transfer and Forward.
Some consider the two the same. Which of course they aren’t.
In short Transfer is the act of taking a call and then transferring it to another location. This could be another extension, telephone user (inside or outside of the organization) or as it may have been for the past 15 years or so, to someone’s voice mail.
To Forward is to have all calls that come to your number forwarded to another number. Presently this in most cases is to your voice mail box.