The term, en plein air, originated with the French Impressionists.  It refers to painting outdoors and capturing the colors of the daylight.  Though most of my work is done in the studio, the subject and composition are captured from life; painting a small plein air piece, painting a model study and/or photographing my experience.  There really is no substitute for painting from life.   A visual memory of the first-hand experience is one of the tools we rely on while painting.