This is an AA ability, and requires previously obtained Communion of the Cheetah, another AA ability.
Communion of the Cheetah is an insta-cast group buff of Spirit of the Cheetah, and eliminates all of the downside of that spell, since it lasts over a minute, does NOT require elimination of any other speed buffs and has a 10-sec recast timer so it can be kept "up" all the time. In fact a druid could hot-key this AA to a button he uses a lot, like the forward button, and keep cheetah on him and his group all the time.
The AA on this page, Hidden Communion of the Cheetah, adds Improved Invisibility to the speed buff. But, like with all invis spells, if you cast, enter attack mode or get hit while it's on, you will lose the buff, which strips not just your invis but also your run-speed benefit. The good news is if you have Flight of Eagles or some other run-buff running, even Hidden Communion does not overwrite or cancel it, so if you lose this buff due to a mob hitting you, you still retain the underlying run-speed advantage. Plus since Hidden also has no recast delay, the druid can just recast it while running.
All in all, two excellent druid AA's, just be aware of the differences. Regular Communion is great for kiting and high-speed movement in "safe" zones while use Hidden to get thru dangerous zones but no casting allowed!
Oh, btw, shamans get this too.
Edited, Sep 2nd 2013 8:56am by Sippin