I've been asked about the term "plein air" many times. It does seem to get thrown around alot. I must clench when someone requests a "plein air frame." It's an incorrect use of the term.
En plein air is a French expression which means "in the open air", and is particularly used to describe the act of painting outdoors. So next time I blog or facebook about plein air painting, you can most likely find me out on a hillside, or down by the lake with my easel and paints. Quite simply put, painting outside.