Recently, Joaquin Almunia, VP of competition policy at the European Commission, took both Nokia and Samsung to task for their behaviors in regards to patent litigation. In a speech, Almunia fired a warning shot across the bow of Nokia, indicating his concerns that the tech company was beginning to act like a patent troll. But, as Tim Worstall points out in a piece he wrote for Forbes, there is such a thing as a patent-assertion entity (PAE), which is not necessarily the same thing as a patent troll.
Almunia cites statistics that show just how bad the patent troll problem is in the United States, but he seems to be using the terms PAE and troll interchangeably. The fact of the matter is that a PAE is any company that chooses to enforce its patents through licensing or litigation. This could include, for example, universities, which often hold many patents that they do not use for, say, manufacturing.