A patent is a legal monopoly,, you have the right to stop anyone from making it, using it or selling the subject matter of the patent for 20 years. In other words a patent it gives the owner of the patent (sometimes inventor of the product) 20 years of inclusive rights to sell, make what ever there product for 20 years with out anyone copping there idea. Prior to the early 1990's it was 17 years. So basically if an item has a Pat. D. 0ct 20 1893 the item could of be made on that date or 17 years after. After that the patent was expired and the products being made no longer carried a date. Hope that helps.