A database is the organised store where a website keeps all its written information — articles, comments, product details, user accounts and settings — neatly arranged so any piece can be found and pulled up in an instant.
Think of a very tidy filing cabinet with labelled drawers and folders: nothing is thrown in at random, so when a visitor opens a page, the site knows exactly which “folder” to reach into for that text. Without this order, finding the right information among thousands of items would be slow and messy.
The database usually lives on the Hosting together with the rest of the site. Because it holds so much of the site’s content, it is one of the most important things to include in a Backup, so nothing is lost if something goes wrong.