Novelty search A "novelty search" is a prior art search that is often conducted by patent attorneys, patent agents or professional patent searchers before an inventor files a patent application. A novelty search helps an inventor to determine if the invention is novel before the inventor commits the resources necessary to obtain a patent. The search may include searching in databases of patents, patent applications and other documents such as utility models and in the scientific literature.
Validity search A "validity search" is a prior art search done after a patent issues. The purpose of a validity (or invalidity) search is to find prior art that the patent examiner overlooked so that a patent can be declared invalid. This might be done by an entity infringing, or potentially infringing, the patent, or it might be done by a patent owner or other entity that has a financial stake in a patent to confirm the validity of a patent.
Clearance search A clearance search is a search of issued patents to see if a given product or process violates someone else's existing patent. If so, then a validity search may be done to try to find prior art that would invalidate the patent. A clearance search is a search targeting patents being in force and may be limited to a particular country and group of countries, or a specific market.
State-of-the-art research State-of-the-art-research is often conducted by a researcher who would like a comprehensive listing of the most recent patents in a certain field, to help guide his research.
Technically, as a patent searcher, you must make sure you are familiar with the search language for the database you are using. Unfortunately, none of the different patent search engines use the exact same search language. If you assume that you can use the same syntax from one patent searching site to another, you are going to have a problem.