Theme and variations on root position

Um, err, "root position" is a technical term in musical analysis. It refers to a chord (another technical term) with the tonic (another technical term) voiced on the bottom of the voicing (another technical term). Gavriil is playing triads, though he is doubling the tonic on the top of the voicing as well as having it on the bottom, so the chord he is playing have four notes. He does other things, too, but mostly he's playing chords in root position, or trying to.