What is the difference between php and mysql?

MySQL

A simple answer is that PHP is a language while MySQL is a software.

PHP

PHP is a interpreted language used mostly for server-side scripting. It uses an interpreter given by PHP.net website used along with apache or anyother server.

It is similar to languages as asp , jsp , python scripts as they nearly perform similar function of serverside scripting.

MySQL

MySQL on the other hand is a database server / client (depending upon which one you get)

The MySQL uses SQL (structured Query Language ) Pronounced as Sequel, To store and retrieve data.

Most developers in web specially php use MySQL on server side, but it is not limited to php it can be used along with almost all the languages to store and retrive data.