It looks like it's a designation for how long/for which notes to hold a barre, or partial barre.
For example 1/3BV, likely means hold a 1/3 barre (i.e. two strings) at the fifth fret. (A "barre" is the act of holding down more than one string with the same finger, usually, but not always, at the same fret. Parkening, for example, used to like to barre diagonally across two frets, fretting some strings at one fret and the others at the next higher fret, using one finger. Barres can be done with any finger, not just the index finger.)
https://en.wikipedia.org/wiki/Barre_chord