what is the meaning of grand bass!?

Answer 1

If ur referring to the italian phrase "basso profundo", it means a really low-pitched bass singer, or his vocal range, especially as far down (low) he's able to sing. That would mean low "C"s and down to & including low "A"s & "G"s - that's an octave brlow the "normal" low "G" as in the note written on the bottom line of the bass clef.

Answer 2

Or do you mean ground bass, which describes the bass line, often played by cello ( viola da gamba ) and cembalo in the baroque period?