Cataloging (also cataloguing) is a practice that falls within the larger field of information organization (sometimes also called as bibliographic control or as organization of information).
The skill (or art) of organizing knowledge (or information) to allow for retrieval or discovery. The process of describing materials and providing the title, creator, subject associations, keywords or tags so that the materials themselves may be discovered and retrieved.
In other words: providing detailed information about information resources, so that people can find the information they need.
Literally, "information about information." Structured information that describes the details of information resources so that those resources can by discovered, accessed, and used.
Metadata works like the soup package here, and includes information like the brand, soup name, flavor, and nutritional information so the patron can determine if this is the soup (or information resource) they need.
The soup is like the book, journal article or other source of information. The goal of cataloging is to ensure that users can find the information (soup) they need.*
The practice and process of creating metadata, assigning subject headings, call numbers and keywords, and maintaining the system through which all this information is made available.
Cataloging includes defining the metadata, or information on the soup package, as well as organizing all that metadata so that information resources (soup) can be easily found and accessed, like organizing and labeling the departments and shelves in the grocery store.
* This analogy courtesy my cataloging professor, Candy Schwartz.
Sources:
Cataloging and Classification by 
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