8va or 8
8va bassa or 8va sotto
ottava, i.e. perform an octave higher than written.
perform an octave lower than written (sotto = under).
place, i.e. (after playing octave higher or lower) resume the playing as written.
play the passage not in single notes, as marked, but in octaves (the added line of octaves will be above if the passage occurs in the treble of a pf. piece, and below if in the bass)