The back-end of a website is the part hidden from view of regular website visitors, behind the scenes, if you will. The back-end enables the front-end experience, handling the information structure and applications.
The back-end is the part of the computer system or application that is not directly accessed by the user, typically responsible for storing and manipulating data.
Think about the front-end as part of the iceberg above the water. It’s what the user sees -- the sleek-looking site. The back end is the rest of the ice; it cannot be seen by the end user, but it is the most fundamental element of a web application. The back-end runs on the server, or, as it’s often called, “server-side”.
This is where we as developers manage the complete website, and where all changes to the finished site are made.
Back-end development is required to create a dynamic site. A dynamic site is a one which is constantly changing and updated in real-time. Most sites are dynamic sites, as opposed to static sites.
Facebook, Google Maps and this blog are all considered dynamic sites. Blogs are dynamic sites, since their content is constantly changing and updating. A dynamic site requires a database to work properly.