Plein air is just the French phrase for outdoors, so it's a fancy way of describing art done outside on location. The original/most common usage is in the context of plein air painting but there's nothing stopping you from using it to describe drawing
I'm doing plein air now???? Is there anything I can't do???? (yes actually) https://kalechips.net/posts/2024-05-22-Plein-Air
I've never heard the term "plein air" before! Is it just observation drawing, or is there more to it?
Plein air is just the French phrase for outdoors, so it's a fancy way of describing art done outside on location. The original/most common usage is in the context of plein air painting but there's nothing stopping you from using it to describe drawing