Kratky is a method of Hydroponics named for its inventory, Bernard Kratky. The system is passive, meaning no pumps of any type are involved to grow plants.
The method involves a plant in a net pot or otherwise suspended in nutrient solution. As the solution evaporates, an air gap forms allowing the roots access to a large amount of air - oxygen is good for plant roots.
The system is best suited for leafy greens and herbs, though generally is not as effective as other means for growing things.
References
https://medium.com/heroic-hydro/how-to-do-kratky-the-easiest-hydroponic-system-9ba148f340e3