Pratyahara
Pratyahara, the fifth limb, means withdrawal or sensory transcendence. It is during this stage that we make the conscious effort to draw our awareness away from the external world and outside stimuli.
Dharana
As each stage prepares us for the next, the practice of pratyahara creates the setting for dharana, or concentration. Having relieved ourselves of outside distractions, we can now deal with the distractions of the mind itself which is not an easy task.
Dhyana
Meditation or contemplation, the seventh stage of Ashtanga, is the uninterrupted flow of concentration. Although concentration (dharana) and meditation (dhyana) may appear to be one and the same, a fine line of distinction exists between these two stages.
Samadhi
Mahrishi Patanjali describes this eighth and final stage of Ashtanga Yoga, "Samadhi", as a state of ecstasy is the highest state of human existence, Only the TRUE YOGI's can only achieve this.