The human resources department at a corporation like Starbucks maintains a lot of structured information. They must keep information on their employees, on their stores, on their products, etc. This type of data is naturally stored in the tables of a relational database. The `employees` table, for instance, would have one row per employee and columns for first name, last name, address, etc. Information is extracted via SQL queries. Links can exist between tables, allowing an executive to quickly retrieve, say, the birthdays of all employees at store #2151.
MySQL is a popular and well-maintained relational database. It is cross-platform, but most commonly run on Linux as part of the LAMP stack. Web frameworks like Django use database back ends like MySQL or PostgreSQL to store their model objects. Setting up a MySQL database is not too difficult, and a program like phpMyAdmin can help with database maintenance and troubleshooting.
These wiki entries are, in fact, stored in a MySQL database and served to you courtesy of Django and the Apache web server!