When we install MariaDB, we're installing a database server, not a specific database, and a single MariaDB database server can have several databases inside it. Here's an analogy that can help us understand this arrangement: a database can be thought of as a large filing cabinet. The filing cabinet contains a number of drawers and inside each drawer are files with information. In this analogy, the filing cabinet is a database, the drawers are tables within the database, and the files are rows of data within the tables. So what is MariaDB? It's the room the filing cabinet is located in, and it's a large room so we can put many filing cabinets inside it.
When MariaDB is installed, the installer creates a system database that MariaDB uses to keep track of users, databases, and other housekeeping information. The installer also creates a test database for experimentation and learning, and a couple of read-only, semi-virtual databases where MariaDB stores performance...