Yoga means stopping mental activity.
Patanjali defines yoga as nirodha, or a quieting of the vrittis (fluctuations) of the citta (mind, intelligence, and ego). ‘Nirodhah’ literally means ‘stopping,’ so ‘stilling’ is a good way to understand this sutra. The word ‘nirodhah’ is cognate to ‘erode.’ ‘The root is rudh — to obstruct. And it seems the vrttis (the whirlings of the mind) are gradually worn away like that — eroded as we become established in our own being.