Grants you access to the /fly command so you can soar through the skies at will - for 24 hours!
(And you get the cool 'Flying Club' name prefix for the duration, too, so everybody knows you're basically a superhero!)
You will receive a voucher in your inventory (White feather icon) which you* can redeem when you decide you want to enable the access to the command and it will expire after 24 hours of activation.
* or give to a friend in-game!
** or sell to a player in-game!
*** or list it on Auction House in-game!