The Oxford Dictionary defines metadata as "data whose purpose is to describe and give information about other data." While one can read this definition and make sense of the words, what exactly does it mean? It's not a particularly useful definition. It's probably more useful to learn about where metadata comes from and what it does.
Metadata is structured information that allows someone to identify, locate and retrieve a resource. The people who work with library metadata are called metadata librarians or catalogers. Metadata librarians and catalogers support research by creating, storing, enhancing, fixing and maintaining the data that describes all types of library resources. Patrons probably rarely see metadata librarians and catalogers, but their work is what allows for users to come into a library or search the online catalog and find something they need. Metadata is the engine that powers the library catalog.
Cross stitch entitled Same Old Message, Different Day by Ann Kardos
Alphabet chart and border design from Improper Cross Stitch by Haley Pierson-Cox (2018)
Sometimes structural and preservation metadata are considered subsets of administrative metadata.
Metadata is a technical skill that anyone can learn. If you'd like to learn more about the basics of metadata, there are some great resources available to UMass and Five College patrons: