Post-Impressionism is a term coined by the British artist and art critic Roger Fry in 1914, to describe the development of European art since Monet.

The term was coined by Roger Fry for the works of Paul Cézanne, Georges Seurat, Vincent van Gogh, Paul Gauguin, Henri de Toulouse-Lautrec, and others.

Exploring Art Style

Most of these painters first pursued Impressionism, a style based, in its strictest sense, on the objective recording of nature in terms of the fugitive effects of colour and light.

John Rewald, one of the first professional art historians to focus on the birth of early modern art, limited the scope to the years between 1886 and 1892 in his pioneering publication on Post-Impressionism: From Van Gogh to Gauguin (1956): Rewald considered it to continue his History of Impressionism (1946), and pointed out that a "subsequent volume dedicated to the second half of the post-impressionist period" - Post-Impressionism:
From Gauguin to Matisse - was to follow, extending the period covered to other artistic movements of the late 19th and early 20th centuries — to artistic movements based on or derived from Impressionism, at all.

Post-Impressionism v/s Impressionism

Post-Impressionism was both an extension of Impressionism and a rejection of its limitations.

Post-Impressionists continued using vivid colours, thick application of paint, distinctive brushstrokes and real-life subject matter, but they were more inclined to emphasize geometric forms, to distort form for expressive effect, and to use unnatural or arbitrary color.

The Post-Impressionists rejected this aim in favour of more ambitious expression, admitting their debt, however, to the pure, brilliant colours of Impressionism, its freedom from traditional subject matter, and its technique of defining form with short brushstrokes of broken colour.

Each painter in the movement pursued unique, personal subject matter and, while sharing stylistic goals with the other Post-Impressionists, had a personal form of expression.

The post-Impressionists were dissatisfied with the triviality of subject matter and the loss of structure in Impressionist paintings, though they did not agree on the way forward.

Georges Seurat and his followers concerned themselves with pointillism, the systematic use of tiny dots of color. Paul Cézanne set out to restore a sense of order and structure to painting. He achieved this by reducing objects to their basic shapes while retaining the bright fresh colours of Impressionism.

Vincent Van Gogh used colour and vibrant swirling brushstrokes to convey his feelings and his state of mind. Although they often exhibited together, they were not a cohesive movement. They worked in geographically disparate regions and in various stylistic categories, such as fauvism and cubism.

Art critic Roger Fry first used the term to describe the Les Nabis group.

In Nutshell

Terminology
Term, which refers to the period after Impressionism, was coined by the British art critic Roger Fry for his 1910 London exhibition "Manet and the Post-Impressionists." The term was invented after nearly all its practitioners had died.
Artists
Paul Cézanne, Georges Seurat, Henri de Toulouse-Lautrec, Vincent van Gogh, and Paul Gauguin.
Timeline
1880s through early 1890s.
Started In
France.
About
Post-Impressionists weren't reacting against Impressionism, they were trying to take the ideas of Impressionism further. They also were not interested in the Impressionist's preoccupation with naturalism and momentary effects. Still, nearly all the Post-Impressionists passed through an Impressionist phase.
Theme
Landscapes, portraits, still lifes, exotic locations, interiors, etc.
Art Style
Since Post-Impressionism refers to a time (the period after Impressionism) and not a style, there are many styles occurring simultaneously. The styles of Post-Impressionists reflected the individual artists' personal emotions and world views, rather than a naturalistic approach to painting.
Known Work
VAN GOGH, Wheat Field and Cypress Trees, 1889.
GAUGUIN, The Vision After the Sermon, 1888.
Inspiration
Impressionism.
Become Inspiration Of
Symbolism, Nabis, Art Nouveau, Fauvism, Cubism, and German Expressionism.