What is a Database
A database is a file (or group of files) that store information in an organized fashion, usually in tables, and allows you to add new data, update or delete existing data, and run queries that retrieve data according to your criteria.
Databases in the Internet world
Databases became a common part of websites with the rise of dynamic content. Every piece of information that your website generates or gathers, either through web forms, file uploads, or scripts, can be saved in one of three ways: sent by email, saved as a file, and saved into a database. Of these three, a database is the most structured and manageable format.
A classic example is a site that allows users to register an account, no matter the purpose. The list of usernames and passwords must be kept somewhere accessible but secure, and easily searched whenever someone types in his login information.
If the data were kept in a single file, you'd have to write complicated script to scan through the file until you find a match, and to modify the file whenever someone joins or changes a password.
In a database, you'll have a Users table with a username column and a password column. A simple query can retrieve all rows with a specific username, and check the password against the one provided in the login form. Another simple query can update a password or a username, delete a row, or add a new one.
Database types
The most common database language is <SQL> (Structured Query Language). Most hosting providers offer SQL-compatible databases. If you consider having any kind of dynamic content in your website, make sure your hosting package includes at least one database.
<Linux hosting> usually offers one ore more <MySQL databases>, usually for no extra charge. Most open-source Internet platforms, like Wordpress, Joomla, Drupal, etc. are based on a combination of <PHP> and <MySQL>.
<Windows-based hosting> usually offers MS-SQL (Microsoft SQL) databases for additional payment, based either on quota (by megabytes) or on number of databases.