(Sanskrit: वृत्ति), literally “whirlpool”, is a technical term in yoga meant to indicate that the contents of mental awareness are disturbances in the medium of consciousness.
Vritti is literally translated as whirlpool or waves, and in this context we mean it as mental waves. What are the mental waves? Well, that is everything going on inside of our mind.
A good way to translate vritti is mental activity. You could say mental waves, but a more practical direct translation is a mental activity because any activity of the mind is vritti. If you’re studying something, writing, thinking about something, that’s vritti. When you sit to meditate and your mind is stubborn, that is vritti causing you to wandering away.
It’s vritti you see when you observe your mind. You’re observing the vritti. That’s all the swirling waves, all the things that are going on inside of ourselves.