Smart components describe "how things work?" and Dumb components describe "how things look?"
Smart components
It will not have DOM markup or styles. It will do the processing and provide the data. It will work like the Controller in MVC.
Dumb components
It is UI only component. It will rarely have own state. If it has, It will have only UI states.
Check medium.com/@dan_abramov/smart-and-dumb-components… for detailed answer.