A quote from Salinger's Zooey:
He put his cigar in his mouth, and, with his right hand, up in the treble keys, he began to play, in octaves, the melody of a song called "The Kinkajou," which, somewhat notably, had shifted into and ostensibly out of popularity before he was born.
Does it mean that he struck two similar notes at the same time, with one note an octave higher than the other?
P.S. What if a player adds his second hand to strike four similar notes across four octaves, would that also be "playing in octaves", I wonder?