What the Word Covers
Post-Impressionism is not a group that met, agreed on anything or exhibited under that name. Tate defines it as the changes in Impressionism from about 1886, which is the year of the last Impressionist group show in Paris.[1]
The name arrived twenty-four years later and from another country. The British artist and critic Roger Fry used it in 1910 for an exhibition he organised in London called Manet and the Post-Impressionists.[1] None of the four painters it is usually applied to had any say in it; two of them were dead by then.
The four are Paul Cézanne, Paul Gauguin, Georges Seurat and Vincent van Gogh, and what holds them together is a starting point rather than a style. Tate's phrasing is that they developed and extended Impressionism in distinctly different directions.[1] They all began from what the Impressionists had established and none of them stayed there.