What Is Cubism ?

Cubism was a highly influential visual arts style of the 20th century that was created principally by the painters Pablo Picasso and Georges Braque in Paris between 1907 and 1914. The Cubist style emphasized the flat, two-dimensional surface of the picture plane, rejecting the traditional techniques of perspective, foreshortening, modeling, and chiaroscuro and refuting time-honored theories of art as the imitation of nature. Cubist painters were not bound to copying form, texture, color, and space; instead, they presented a new reality in paintings that depicted radically fragmented objects, whose several sides were seen simultaneously. Typical cubist paintings frequently show letters, musical instruments, bottles, pitchers, glasses, newspapers, still life, and the human face and figure.

The period from 1910 to 1912 is referred to as Analytical Cubism. Paintings executed during this period showed the breaking down, or analysis, of form. Right-angle and straight-line construction were favored, though occasionally some areas of the painting appeared sculptural, as in Picasso's "Girl with a Mandolin" (1910).

Interest in the above subject matter continued after 1912, during the phase called Synthetic Cubism. Works of this phase emphasize the combination, or synthesis of forms in the picture. Color is extremely important in the pieces' shapes because they become larger and more decorative. Smooth and rough surfaces are contrasted with one another; and frequently non-painted objects such as newspapers or tobacco wrappers, are pasted on the canvas in combination with painted areas.

Cubism is a style of painting which emerged around 1907-1910.  Cubism rejects colour and instead favours the form as being the central point of the painting.  The srtucture of the subject is the focal point, not how it looks.  Picasso was one of the first exponents of cubism.   
A feature of cubist paintings is often several views of an object, which is then broken down into planes or layers.  These layers can sometimes be endlessly repeated, so the final painting looks nothing like the original object which was painted.   The paintings do, however, look very sculptural and are very distinctive.
Juan Gris was a Spanish artist and intellectual who wrote about Cubism and how it linked into scientific developments.  Before this art had always been seen as very separate from other issues and Cubism is an important foundation posts for Modern Art, following on from the post-Impressionists and preceding Expressionism.