The French describe the practice of painting outdoors as “peinture en plein air,” roughly translatable to “painting in the open air.” When it arrived, this was a pretty revolutionary practice in European painting: earlier landscape painters might make sketches while out of doors, but the finished painting would always be worked up back in the studio.
Nineteenth-century painters, most famously those who would come to be dubbed “Impressionist,” committed to completing their landscape paintings on the spot, spurred by their interest in capturing the freshest image of the modern world (and enabled by the invention of highly portable tubes of paint). With their goal of capturing the fleeting particularities of light, the Impressionists had to work quickly. Consequentially their canvases are usually modest in size, and of course feature the characteristic loose brushwork that inspired the Plenaire types.