Conceptural Art
Conceptual art focuses on the concept or idea of the art not the actual object. So the concept may be as simple as “a red wall,” but can be much more complex. Conceptual art was founded by Sol LeWitt. Part of his philosophy was founded by a early job of his as a draftsman (draughman) for the architect, I. M. Pei. In architecture the architect would come up with the concept of the building. This concept would be translated by the the draftsmen into a set of drawings that would be used by the builders to actually construct the structure. The architect may be involved with the high level designs, but not the low level designs and certainly not the fine art of driving a nail into a board so the board will not split over time.
LeWitt wanted to bring that same philosophy to art. He found that executing his ideas took too much time and that he could quickly come up with concepts that others could execute (and perhaps execute better than he could). He also worked on wall paintings where the entire wall would be used for his art. This made it nearly impossible to move his art. So he only sold the concept. If you wanted a Sol LeWitt you can buy a certificate which states that you are the owner of a specific concept and you are allowed to execute that concept on one wall of your choice. You can decided to execute it on another wall, but the first wall is no longer a LeWitt, only the second wall with its certificate. You can sell the concept certificate and your wall is no longer a LeWitt.
LeWitt encouraged copy cats. They did not have the certificate and therefore were not infringing on his concepts. Even two implementations of one of his concepts would be different. The wall would have different dimensions, textures, colors, lighting, spacings, widths, etc. So the only way to know if you have a genuine LeWitt work of art is to see the certificate of the concept issued by the artist and how it corresponds to the installation.