Mysql also known as “My Sequel” is an open source relational database management system.It is based on SQL(Structure Query Language) which is used for adding, removing, and modifying information in the database. Standard SQL commands, such as ADD, DROP, INSERT, and UPDATE can be used with MySQL..

Its mostly related to PHP development environment bcos it also released GPL lcence like PHP.
A website that uses MySQL may include Web pages that access information from a database. These pages are often referred to as “dynamic,” meaning the content of each page is generated from a database as the page loads. Websites that use dynamic Web pages are often referred to as database-driven websites.