In the guitar tab of Opus 35, No 22 in B minor of Fernando Sor that I get from classical clef, there is a notation BII as shown in the above picture.
What does it mean?
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The 'BII' is instructing you to bar your finger across the second fret like you would with a barre chord.
The 'B' stands for bar and the 'II' represents the second fret. You can even see in the sections where the 'BII' occurs the lowest notes on your fret board are on the 2nd fret. This is just a another instruction similar to that of a fingering that isn't "necessary", but helps you play the part.