a state of freedom from emotional disturbance and anxiety; tranquillity.
"Ataraxia should act like a slow-release drug, accumulating over days and weeks. Ancient philosophers believed achieving ataraxia created an emotional homeostasis, where the effect wouldn’t just be a more stable base-level mood, but one that would hopefully flow out to the people around you. If you are more tranquil, you will be less likely to react or combust. So not only do you not ruin your own day, you avoid ruining other people’s too. In a tranquil state you may even make better decisions."
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.