A biplane. A plane is a wing, or airfoil. Bi means two. A biplane has two wings, one above the other. This plane has the top wing to the rear of the lower wing. Staggered. So it is called a staggerwing.
I was fortunate enough to fly, very briefly, a staggerwing Stearman. It flew like a Cadillac, beautifully, comfortably.
Yes, there were triplanes and I've been lucky enough to see one fly. The most famous of the triplanes is probably a Fokker, the kind Manfred "Red Baron" von Richthofen flew in World War I.
Do people call single wing aircraft monoplanes? Sometimes. Now they're most commonly referred to as fixed wing. Fixed wing as opposed to a helicopter which I'm sure you know also has airfoils, like an airplane, but they are not fixed, they spin around very fast.
So much for your lesson on aviation.