While the time horizon of these two descriptions could overlap, the second description implies that time horizon is somewhat longer and that the asset purchases may not come to an end after two years. Thus, these two descriptions are mutually non-exclusive.
A review is provided in Ben S. Bernanke (2012), “Monetary Policy since the Onset of the Crisis,” speech delivered at “The Changing Policy Landscape,” a symposium sponsored by the Federal Reserve Bank of Kansas City, held in Jackson Hole, Wyo., August 30-September 1. BIS central bankers’ speeches  5  developments in a manner that reduces or blunts potentially harmful consequences.