Yoga Sutras 3.9
Patanjali, explained by Swami Vivekananda
व्युत्थान-निरोधसंस्कारयोरभिभव-प्रादुर्भावौ निरोधक्षणचित्तान्वयो निरोध-परिणामः ॥
vyutthāna-nirodhasaṃskārayorabhibhava-prādurbhāvau nirodhakṣaṇacittānvayo nirodha-pariṇāmaḥ
By the suppression of the disturbed impressions of the mind, and by the rise of impressions of control, the mind, which persists in that moment of control, is said to attain the controlling modifications.
In plain words: When restless thoughts are pushed down and thoughts of control rise up, the mind enters a state of control. This is not yet complete stillness, because the act of controlling is itself a thought. Still, it is much closer than a busy mind.
Swami Vivekananda explains
That is to say, in this first state of Samadhi the modifications of the mind have been controlled, but not perfectly, because if they were, there would be no modifications. If there is a modification which impels the mind to rush out through the senses, and the Yogi tries to control it, that very control itself will be a modification. One wave will be checked by another wave, so it will not be real Samadhi in which all the waves subside, as control itself will be a wave. Yet this lower Samadhi is very much nearer to the higher Samadhi than when the mind comes bubbling out.