Plein air is from the French. Plain air. It means to draw or paint outside in the open air. Technically LaChapa didn't do plein air since it is inside. Those small portable easels are perfect for it. Monet and Renoir did plein air paintings. Early painters tried to capture the natural light in some of those famous paintings of water lilies, haystacks, etc. The next time you go to the museum, stop and really look at one of them for a couple of minutes. You can possibly tell the time of day, or feel the breeze or the water moving.
Actually, it's outside on my patio. Was hoping to get out to an "open" area, but the timing for that proved more challenging than expected. I guess that's the cost of city living. I would have gone downtown if I was any good at drawing buildings.