Some context might help. Grasshopper is testing systems that are being developed to recover the first stage of the two stage Falcon 9 launch vehicle. It is built from a Falcon 9 first stage with all but one engine removed. Falcon 9 has already reached orbit 6 times (5 times with the version that the current Grasshopper vehicle was built from, and most recently just a couple of weeks ago with an upgraded version).
SpaceX is developing a fully reusable launch system, in which both the first and second stage return to the landing site after being jettisoned, rather than discarded like in currently operational launch vehicles. Here is an animation showing how the Falcon 9R will work. http://www.youtube.com/watch?v=sSF81yjVbJE (the animation is a bit out of date, since it is based on the old Falcon 9 v1.0, which has been superseded by the newer v1.1, which is longer and has its 9 engines in a different configuration).
This may be the last flight of this vehicle, as a newer version of Grasshopper has been built using a v1.1 first stage. While Grasshopper has been testing the landing phase of the first stage recovery operation, SpaceX has also been testing other end of the operation. In the maiden flight of Falcon 9 v1.1 just a couple of weeks ago (which successfully deployed a Canadian satellite called CASSIOPE), they attempted to fly back the first stage to make a "soft" touchdown in the ocean. Unfortunately, the stage ended up spinning too fast, which choked off fuel from the engine. Apparently in the final version of Falcon 9R, the landing legs will act as spin stabilizers as well, which this launch vehicle did not have.
A good overview of current plans for developing the reusable Falcon 9, which I find immensely exciting, can be found here: http://www.nasaspaceflight.com/2013/10/musk-plans-reusability-falcon-9-rocket/