Hi Arturo, good to see you on the iris thread. It's not nice of us to use these abbreviations without an explanation. But we get too lazy to type out all the words. I think Texting is making things worse!
PBF stands for Purple Based Foliage. Some irises have purple coloring at the base of the leaves. Some have a lot, others have a small amount, and still others have none at all. Some have purple that shows on the stems of the bloom stalks and some have purple on the bloom spathe.
I don't have a good picture of PBF, but here's a picture of a purple spathe on the iris Dialect. You can see a tiny bit of PBF on one leaf though. Wish I had a better picture.
I'm sure some one will have some to add.