A 'duo concertant' comes from Italian “in stilo molto concertante,” which implies the two performers are equal, dynamic voices. A little different from a duet, as both voices (in this case two pianos) carry equal importance throughout. It's not a 'concerto' where a soloist plays in a virtuoso manner. There's a small chamber orchestra; it's a theme and variations.

(The pic is from Iceland, which we visited in June 2024. If you ever get a chance to travel there - go!)