Concentration / dhyana = dhârana = meditation
The concentration is an act : I concentrate on one or several objects, the breath, the display(visualization), a sound etc.
The meditation is a state: " I fall " in meditative state following something, following an act, behind a breath, a concentration at the moment, something awakened me, sublimated the state of concentration in meditation, in pondering.
« Drona, a Fencing teacher, taught the art of the archery to the brothers Pandavas, the famous heroes of the Mahabharata. One day, Drona had installed(settled) a wooden fish on the highest branch of the highest tree of the place of training. Five Pandanvas was held there, ready to try, at the request of Drona, to achieve with their arrow, said fish.
Drona called the first one of the brothers and asked him(her) before he pulls(fires): « friend, whom do you see? » « I see the blue of the sky, the tree, the wind in banches, fish » he answered "." Indeed, answered Drona, then put your bow(arc) and does not pull(fire) ».
He called the second and asked him(her) before this last one pulls(fires): « friend, whom do you see? ». « I see the tree, the branches, the branch on which is the fish, the fish » answered this last one "." Indeed, answered Drona, then put your bow(arc) and does not pull(fire) ».
He called the third and asked him(her) the same question: « friend, whom do you see? ». « I see the tree, the branches, the branch, the sheets(leaves), the fish » answered this last one ». And Drona ordered the same thing(matter). And so on, no prince not pût to pull(fire) his arrow.
Drona called finally Arjurna and asked him(her) the same question; Arjurna answered: « I see only the eye of the fish and anything else ». Drona says to him(her) then; « adjust your bow(arc) and pulls(fires) ».
Arjuna, illustrious archer of the Bhagavad Gîta
Dhârana is the consciousness of the mental on an object of concentration, that they are outer(foreign) or that they are internal as chakrâ or physical, mental zones.
DhyanaThe state of Meditation comes when Dharana is continuously maintained. But more still, this state is maintained when the mental is not interrupted by the waves of thoughts (Vritti).
Dhyana it is so nevertheless this state where we are still conscious that we meditate.
The object of meditation can give the impression(printing) to disappear, but the consciousness of the practice stays.
Even there, there are various levels degrees in the experience(experiment), and they depend in fact on the presence of the duality.