I would consider a "fine" print to be what at the time you consider to be the best print you can produce from a negative. That is not to say at a later date you would not have a new interpretation of the negative.

A fine print I think also means one that is archival, and at least mounted in a way that presents your work the best possible way. I don't think it has to be over matted and framed, but I don't believe that a final print sitting in a box is a fine print.