Post-Impressionism refers to a loose group of artists in the late 19th century who were influenced by Impressionism but developed their own unique styles. These artists, including Paul Cézanne, Paul Gauguin, Vincent van Gogh, and Georges Seurat, experimented with techniques like pointillism, distortion of color and form, and symbolic content to convey emotion. Their works moved beyond Impressionism to focus more on design and emotion, laying the foundations for 20th century modern art movements like Cubism and Expressionism.