Overt Software support of MySQL stems back from its early days in supporting Moodle Virtual Learning Environment (VLE).
MySQL is a database system used on the web. Basically, a MySQL database allows you to create a relational database structure on a web-server somewhere in order to store data or automate procedures.
If you think of it in comparison to Microsoft Access, MySQL is what holds all of your tables, PHP acts as your queries (among other things), and your forms are basically web pages with fields in them. So with all these open source products combined, Overt can create truly spectacular web solution affordable for your business needs.