A SAS Catalog is a special kind of SAS file. If, for example, you ever use SAS macro language to create a macro program, or create SAS formats or create SAS/Graph output, then SAS catalogs are being used behind the scenes.
If you follow this path in the SAS Help files:
Contents --> Using SAS Software in Your Operating Environment
--> Glossary --> pick your operating system --> Glossary
In the glossary, you will find a basic description of a SAS catalog and a SAS catalog entry. For example, here is the Windows glossary entry for catalog:
a SAS file that stores many different kinds of information in smaller units called catalog entries. A single SAS catalog can contain several different types of catalog entries. See also SAS catalog entry.
SAS catalog entry
a separate storage unit within a SAS catalog. Each entry has an entry type that identifies its purpose to SAS. Some catalog entries contain system information such as key definitions. Other catalog entries contain application information such as window definitions, Help windows, SAS formats and informats, macros, or graphics output. See also entry type.
A SAS catalog will have different operating characteristics (for example, if you needed to allocate them on MVS or z/OS), so before you change or move a SAS catalog, you should be careful to read about how your operating system stores catalog information.