A database is a governed network of digital media items which have been semantically linked to each other according to a specific format.
Database is distinguished here as a governed network to distinguish it from linked data, which is a more expansive term. Database is nonetheless an extremely generic term; however, specific database formats often have strictly detailed specifications, usually based on rules for connecting media items and tables to each other.
Note that it's possible to create "distributed databases" which connect the data and databases of autonomous projects, if those connections meet the standards of a standards governance project. (If standards governance is either undeveloped, or ignored, it arguably makes more sense to refer to a holographic or semantic web, or distributed networking, than to use the term 'database' at all.)