A database is an organised collection of information managed by a database management system (DBMS). Joomla stores articles, users, categories, settings and extension data in its database.
Tables, relationships and indexes
Relational database tables contain rows and columns. A primary key identifies a record, while identifiers connect entities, such as an article and its category. Indexes speed up searches but take space and must be maintained when data changes.
SQL is used to query and modify data. Transactions can group related operations into a consistent action when supported by the storage engine.
The Joomla database
Joomla connects to a DBMS using a database name, user account and server settings. A table prefix distinguishes sets of tables, but is not a security control by itself.
A Joomla backup needs both database contents and files. Images normally reside in file storage, with references kept in the database. Before manual table changes, create a backup and verify recovery. Routine editorial changes are better performed through the application interface.
Conclusion
A database holds website structure and state. Maintenance includes access control, DBMS compatibility and tested backups.