In short, “prior art” is information that existed before a certain date. That information is either (a) available to the public or (b) treated as available by the law even if it is not. The more detailed explanation follows. In modern popular terminology the word “art” has come to be limited to the various branches of creative activity, such as painting, music, literature, and dance or the expression of skill in one or more of those branches. But, as used in the patent field, “art” still has its more generic, but now somewhat archaic, meaning of a field of knowledge – typically one in which skill and knowledge is acquired through practice. The word “art” is still used today in patent law because the original U.S. Constitution gives Congress the power to create a patent system in order to “To promote the progress of science and useful arts”.

As used in patent law when applied to utility patents the term “art” means the knowledge in a field of science, technology or engineering. When applied to design patents the term “art” means knowledge in the more modern meaning of a field of creative activity when applied to the ornamental, non-functional appearance of useful article of manufacture.

“Prior” has the usual meaning of “before”. But the difficult question arises: “before what?” The basic principle is that an invention should be an advance or improvement of the art, and a person should not receive a patent for technology that was previously known by people skilled in the art. The invention should be an advancement beyond the art that existed prior to the invention. The modern general application of that principle in the United States is that prior art is the state of the field of knowledge in the art before either an invention was made available to the public by the inventor or before a patent application was filed for the invention. But, with regard to the inventor making the invention public, the law gives the inventor only one year from making the invention public. If the inventor makes the invention public more than one year before filing a patent application, the inventor’s own disclosure to the public is prior art thereby destroying the inventor’s right to get a patent. If the inventor makes the invention public less than one year before the inventor files a patent application, public information after that is not prior art. This one year period applies only to the United States and a few other countries.

As can be seen from the preceding paragraph, it can be difficult and complicated to precisely determine when a patent, commercial act or other public disclosure of technology is prior art to a particular invention. Prior art includes information that was publicly disclosed before the filing date of your patent application, except that it does not include information disclosed by the inventor or by someone who derived the information from the inventor, as long as the information was first made public less than one year before the filing date of the inventor’s patent application. The prior art includes published materials throughout the world in all languages, and is not limited to patents. Prior art also includes technology contained in products that were on sale or publicly disclosed before the inventor’s application filing date by someone other than the inventor. In many circumstances the prior art also includes information in patent applications filed anywhere in the world before the inventor’s application filing date even if the application which is prior art could not be found in a search because it was kept secret at the time the search was performed.