Plein air painting refers to the practice of painting outdoors, capturing the natural light and atmosphere of a scene directly from life. This technique emphasizes spontaneity, immediacy, and the transient qualities of light, which are essential elements in conveying the artist's interpretation of the landscape or subject matter. Plein air painting played a significant role in shaping movements that focus on realism and impressionism, as artists sought to depict their surroundings with authenticity and emotion.