Gliders were introduced June 24, 2011. Players will need to complete the Glider Mount Quest Series.
Gliders move on the ground at about 60-75%, compared to ground mount speeds of 130-135% base. 
Gliders are available to players at levels 60+. Gliders don't leap up as far, but once they catch air, they can cruise a long way before stopping. Launching from a high point can let you sail all the way across a zone before you hit the ground.
To "catch air", run in the direction you want to glide then press Jump (spacebar) and hold Forward and Jump down, causing your glider mount to leap powerfully and rise. When the glider reaches cruising altitude it will level out and you will see flaps extend from it's sides. At this point you can release the Jump key. Releasing Jump before the flaps extend will drop you immediately, resulting in little more than a powered "hop".
Pressing Jump again while in Glide mode will cause you to close the glide flaps and cause you to descend rapidly. Pressing Jump can also re-open the flaps.
While gliding, avoid any sudden left/right movement. Gliders require a gentle touch to steer and there is very little we can say here to teach you, it just takes practice.