Here is the FEI definition of what is required for a passage ( pronounced pasahhje)
The passage is a measured, very collected, elevated and cadenced trot . It is characterized by a pronounced engagement of the hindquarters, a more accentuated flexion of the knees and hocks and graceful elasticity of the movement Each pair of diagonal legs is raised and returned to the ground alternately, with cadence and a prolonged suspension.
FEI Article 414
There is more to that article 414 but suffice to say here is a video of Belinda Trussell riding my horse Biasini in passage. She is working with him and training him to do this movement. I added music just for fun! Click “Full Screen” for the best view
It is a joy for me to see my horse working like this. After Belinda had done this passage work I got on and did a few times around the arena in sitting trot. Biasini was electric and this is one of the magical things about getting on after he has been doing this kind of work. Belinda did not ask me to do the passage she just wanted me to feel Biasini in his Electric Mode.
HorseAddict 
I’d love to hear from you!