What is the difference between the Internet and the World Wide Web?

There is a difference between Internet and World Wide Web. Basically World Wide Web is a subset of the Internet. WWW is information space, where each resource is defined as URL and it uses Internet as lower layer, also TCP protocol as a Transport layer.

On the Application layer WWW is using 2 protocols: HTTP - TCP port 80 and HTTPS - TCP port 443. HTTP stands for Hypertext Transfer Protocol,  HTTPS is similar just one difference being secure.

On the other hand, Internet is being used not just by HTTP, also FTP (File Transfer Protocol), SSH (Secure Shell), VoIP (Voice over Internet Protocol)..etc.

To make even clear, you connect to WWW using browsers like Firefox, Internet Explorer, Chrome. But you have many applications that use Internet like Skype, Browsers, Telnet, Games, FTP client, Mail clients .. etc.