Yoga sutra 3.4 states: trayam ekatra samyama: The three [dharana, dhyana, and samadhi] as one is called samyama. The last three limbs of the eight limbs of yoga are considered those limbs that happen naturally, whereas the first five limbs are actively practiced.
Dharana, or concentration, is the process of fixing the mind on one object. Dhyana is the sustaining of dharana for a long period of time. And samadhi is the process of that sustained concentration completely absorbing the concentrator such that the concentrator and the object become one. Together, these three rungs are known as samyama.
Once samyama is achieved, one has full awareness that they are not their body, mind, or anything else physically conceivable. They are also aware that anything they encounter in the physical world is not as it seems. Samyama is a state of enlightenment, and is usually attained after long periods of time spend in meditation.