In meditation, when observer, act of observing, and object of observation collapse into oneness, this is samadhi, the 8th and final limb of yoga. According to the Yoga Sutra of Patanjali, attention leads to concentration (dharana), which leads to meditation (dhyana), which leads to complete absorption (samadhi).
When only the essence of that object, place, or point shines forth in the mind, as if devoid even of its own form, that state of deep absorption is called deep concentration or samadhi, which is the eighth rung. – Yoga Sutra 3.3
Experiencing samadhi results from devoted practice of the various stages of the eight limbs of Ashtanga over a long period of time. Only when concentration can be sustained for a prolonged period without distraction, can the deep stillness and insight of meditation happen. Only when meditation can be sustained with sufficient intensity for clear seeing, can the circumstances be ripe for samadhi. The practices build upon one another and the practitioner matures throughout the process, gaining skill and wisdom.
Even though samadhi is the final limb of Ashtanga, it is not the end of the path. Instead samadhi is yet another tool with many of its own stages. The highest stage of samadhi is said to be effortlessly achieved and sustained – a state of luminous clarity. With diligence and devotion, may your practice one day bring you to highest samadhi!