Plein air painting is painting outside in the open air. Plein air is a term that is derived from the French phrase "en plein air," which is translated as "in the open air."
Plein air painting is largely associated with, and first made popular by, Impressionist artists in the late 1800s. These artists left their studios to go out into nature to capture the effects of sunlight and how the changes in light influenced the colors of a subject. This was a time when artists were beginning to paint subject matter that was not normally seen, such as people engaged in routine activities.