A descriptor in chemistry is like a label that scientists give to different chemical compounds to describe what they are like. For example, you might describe a chemical as "smelly" or "yellow" or "strong". These labels are called descriptors because they help you understand what the chemical is like and how it behaves.
Just like how you might have a nickname that describes you, chemicals have descriptors that describe them. Scientists use these descriptors to help them remember which chemicals do what and how they act. So if a scientist wanted to know which chemical was sticky, they would look for the one that had the "sticky" descriptor.
Overall, descriptors in chemistry are a way for scientists to quickly and easily describe the different properties of different chemicals so they can understand them better.