Final answer:
CAS numbers in chemical databases represent structural information.
Step-by-step explanation:
A unique feature of CAS numbers in chemical databases is that they represent structural information. CAS numbers, also known as Chemical Abstracts Service numbers, are unique identifiers assigned to chemical substances to provide a standardized way of referencing them.
These numbers help to ensure that there is no confusion about the identity of a compound, as they describe the specific arrangement of atoms in the substance.