Those who own but do not practice their patents are sometimes referred to negatively as "trolls" or "patent trolls," especially when they assert their patents against companies who are alleged to be practicing the inventions without a license. Well-known (in some circles) firms that are often identified by others as patent trolls include Acacia Technologies and Intellectual Ventures.
The term was coined in the 1990s. A Wikipedia discussion of the term's origins can be found here. A more, but not completely neutral term is Non Practicing Entity, or NPE.
Patent Kinetics has worked with a number of patent owners who are not clearly either trolls or operating companies. For example, we've worked with inventors who for whatever reason were not able to get funding to bring product to market yet whose inventions were being practiced by others without a license.We helped initiate a law suit against a number of parties that was resolved to our client's satisfaction.
We've also worked with companies that had product in the market but were not able to compete effectively or were . Here, too, their inventions were being practiced by more established companies without a license.
Lastly, there are inventions that are essentially "component technologies," inventions that are useful, novel, etc. but don't deserve their own business devoted to practicing the invention. (I suspect a large majority of inventions entail component technologies.) Here, too, established companies can sometimes be found practicing these inventions without a license. Are these patent owners to be labeled as NPEs or trolls with the usual negative connotations? I hope not.