A dropper is the part of an irrigation system that looks a bit like a plastic pen and drops the water in your substrate.

Learn all about watering cannabis plants:

• When And How To Water Cannabis Plants
• When To Water Your Marijuana Plants
• Watering Marijuana Grown In Soil
• Absorption Of Water And Nutrients By Marijuana Plants

More water related definitions:

pH / Acidity | EC (Electric Conductivity) | Irrigation system | Water temperature