Metadata provides important information about digital content. There are three main places metadata is stored in an EPUB file: the navigation file, packaging file, and HTML files. The minimum required metadata for an EPUB includes a unique ID, title, and language. Additional recommended metadata includes date, publisher, rights, creator, contributor, and attributes for author and contributor roles and names. Metadata in InDesign allows for entries like the identifier, author, title, description, keywords, copyright, and language.