a library catalog is metadata because it describes publications.
Examples of metadata
metadata
Whatever their origin, the metadata labels can then be used to do useful things.
From the economist.com
Metadata and file data are organized into tables similar to relational database.
From the en.wikipedia.org
This is much more effective than the old method of text-based metadata indexing.
From the techcrunch.com
The result is a messy clump of metadata that dwarfs the data in the poem itself.
From the forbes.com
Users who browse the data warehouse are primarily viewing the business metadata.
From the en.wikipedia.org
Some raw files contain a standardized metadata section with data in Exif format.
From the en.wikipedia.org
It is also useful to distinguish metadata, that is, a description of other data.
From the en.wikipedia.org
There's some metadata analysis, she says, but its mostly based on image analysis.
From the techcrunch.com
The images are tagged with metadata that matches an advertiser's product profile.
From the mediadecoder.blogs.nytimes.com
More examples
Data about data; "a library catalog is metadata because it describes publications"
Metadata is the name of a US corporation and a registered trademark in the United States.
Data that describes other data, serving as an informative label
Data that describe a dataset to allow others to find and evaluate it.
File structure information such as file attributes, extent maps, and fileset attributes.
Information about content that allows it to be stored in and retrieved from a database.
In general, "data about data;" functionally, "structured data about data." Metadata includes data associated with either an information system or an information object for purposes of description, administration, legal requirements, technical functionality, use and usage, and preservation. . ...
Contains information about images and other data types. Metadata can include the camera used to take an image, settings used and keywords.
Data that describes other data. For items in open access repositories, this usually consists of a full bibliographic reference, abstract, keywords, and similar information.