Okay, imagine a hot pot sitting on a stove. When you heat up the pot, steam or water vapor starts to form. You might notice that some water droplets form on the lid or edges of the pot. This is dropwise condensation!
Basically, when water vapor touches a cool surface (like the lid of the pot), it turns back into liquid water. This happens in two ways: filmwise (really thin layer of water) or dropwise (big droplets of water).
In dropwise condensation, the water droplets are larger and more spread out. This happens when the surface is really smooth and clean. When water droplets form, they can roll down the surface and take the heat away with them.
Scientists are interested in how to make dropwise condensation happen more often than filmwise condensation. Dropwise condensation is more efficient at cooling things down, and it's also better for creating water droplets for things like fog machines or air conditioning units.