What do the letters M.F.D. stand for on a wine cubitainer?

It means- Mean Fractal Dimension -according the free dictionary

While those initials could stand for a wide range of things, I haven't found onee that makes sense in relation to a cubitainer. A wine cubitainer is a plastic bag inside a cardboard box used to hold wine in a range of volumes, and dispense it through a valve opening. (They appear to be an improved version of the ubiquitous, at least here in Australia, wine casks, a common way to buy cheap wine.) Because they are airtight, they allow a small amount to be dispensed, with the remainder having a significantly longer shelf-life than an opened bottle of wine.

http://www.thebrewshop.com/contents/en-uk/d159_Cubitainers_and_Polypins.html

As it is a registered American trademark product, I haven't got one on hand to look and see where the letters M.F.D. might appear. That might be a clue as to their intended meaning - it could relate to the plastic used, the cardboard box, the dimensions, etc. The only initialism I see online is LDPE, referring to the type of plastic used.

http://www.hedwin.com/products/cubitainer/cube-features

LDPE stands for low-density polyethylene.

https://en.wikipedia.org/wiki/Low-density_polyethylene

Most likely it is "Date of Manufacture"

If you "Google" an image search for "M.F.D on packaging" you'll find numerous examples.