This longest section of the patent describes the invention in detail. It describes each of the features of the invention and how to practice the invention, that is how to make the invention, and how to use it. The detailed description of most patent applications in the biology and chemistry fields contains several examples. The examples describe in great detail how a biological or chemical invention is made. In a patent claiming a recombinant protein, there may be examples describing the growing of suitable microorganisms to be transformed, plasmid construction, isolation of DNA, transfection of the microorganisms, expression of the protein, and isolation of the expressed protein.
Examples typically describe what an inventor has actually done in making and using the invention.
The last paragraph of the specification typically is a statement that the invention is not limited to what is described, but also includes undescribed equivalents of the invention that is recited in the claims. Because the claims define the invention that is protected by the patent, they are in some ways the most important feature of the patent. They provide guidance to competitors in steering clear of the patent. They indicate the scope and bounds of the patent so that a court can determine if the patent is infringed. The claims follow a set format with an unusual grammatical style that is sometimes difficult for non-patent professionals to understand.