El Lissitzky developed a suprematist style of his own, a series of abstract, geometric paintings which he called Proun (pronounced "pro-oon"). The exact meaning of "Proun" was never fully revealed, with some suggesting that it is a contraction of proekt unovisa (designed by UNOVIS) or proekt utverzhdenya novogo (Design for the confirmation of the new). Later, El Lissitzky defined them ambiguously as "the station where one changes from painting to architecture."
Proun was essentially El Lissitzky's exploration of the visual language of suprematism with spatial elements, utilizing shifting axes and multiple perspectives; both uncommon ideas in suprematism. Suprematism at the time was conducted almost exclusively in flat, 2D forms and shapes, and El Lissitzky, with a taste for architecture and other 3D concepts, tried to expand suprematism beyond this. His Proun works (known as Prounen) spanned over a half a decade and evolved from straightforward paintings and lithographs into fully three-dimensional installations. They would also lay the foundation for his later experiments in architecture and exhibition design. While the paintings were artistic in their own right, their use as a staging ground for his early architectonic ideas was significant. In these works, the basic elements of architecture — volume, mass, color, space and rhythm — were subjected to a fresh formulation in relation to the new suprematist ideals. Through his Prouns, utopian models for a new and better world were developed. This approach, in which the artist creates art with socially defined purpose, could aptly be summarized with his edict "das zielbewußte Schaffen" — "task oriented creation."
From Wikipedia sort of.
A Story of Two Squares (1920)
Dlia golosa (1923)