There is a distinction made between, savitarka samādhi, when the samādhi is still ideative: it has still the roots of vibrations, even when there is a silence, it has still the seeds of activity. But there is a higher samādhi : niścalā samādhi; complete cessation, not even seeds of activity.
If you read Sri Ramakrishna’s experiences, he used to enter into samādhi state, to such an extent, that even if you shake the whole body, there is no awareness in that consciousness of the shaking. Even if you speak loudly, or even if you have drum beaten around you, the consciousness is so much absorbed in silence, that none of these things make an effect on you. In that state, many yogis depart from the body, and they attain to a state from which there is no return. This is what is called samādhi in the yoga system of Patanjali.
Here you find:
śruti-vipratipannā te yadā sthāsyati niścalā |
samādhāv acalā buddhis tadā yogam avāpsyasi ||53|| (II)
Here also there is a mention of niścala, something which is completely motionless: niścalā; samādhāv acalā buddhi: buddhi when it becomes acalā, samādhāv, in the Samadhi.
Here there is a complete identity with the description given in the yoga of Patanjali and description given here. That when your buddhi becomes acalā, completely stabilised, in that state of trance, then you will attain to Yoga. But surprisingly Yoga here means the Karmayoga; you will be able to perform action, and the right action, faultless action. This is not in the classical philosophy of Yoga.
It is the emphasis is upon withdrawal from action, and you become withdrawn. Whereas here, it is said: “samādhāv acalā buddhis tadā yogam avāpsyasi”. Yoga actually, as Sri Krishna says: “By Yoga I mean the Karmayoga, and you will attain to yoga when your buddhi, your intelligence, becomes completely stabilised in samādhi”.
Then is the famous question of Arjuna, which triggers off the answer of Sri Krishna, which is one of the most important illuminating answers in the Bhagavad Gita. I propose to read this whole thing, so that textually you have a concrete idea of what the Gita means by samādhi. In 2nd chapter, verse 54, Arjuna asks this question:
sthita-prajñasya kā bhāṣā samādhi-sthasya keśava |
sthita-dhīḥ kiṁ prabhāṣeta kim āsīta vrajeta kim ||54|| (II)
sthita-prajña: that is to say, one whose prajña, his intelligence, has become stabilised, of that, kā bhāṣā, how does he speak? One who is in samādhi, one who is samādhistha, (stha means that which is sthira), that which is established in samādhi, one whose prajña is sthita, so: sthita-prajñasya samādhi-sthasya kā bhāṣā.
“O Keshava, keśava, what is the language? How does he speak? One who is established in prajña is sthita, and one whose consciousness is in samādhi, sthitadīḥ, one whose intelligence is again stabilised sthitadīḥ kiṁ prabhāṣeta, how does he speak? kiṁ prabhāṣeta, how does he sit? vrajeta kim, how does he walk about?”