Drupal is a free and open source content management system (CMS). A CMS is a software that allows you to manage the content of a website. This allows users to change the site without resorting to a programmer.
Drupal is a tool that caters to both beginners and experts programmers. Its flexibility allows it to respond to the vast majority of market needs: corporate websites, blog, directory, community, merchant or intranets, anything is possible.
Speed of implementation
Drupal allow to develop a practical and scalable website, in a few clicks, without writing a single line of code.
We can extend the possibilities by adding modules. These are very numerous, proposed by the community and always under GPL license.
This architecture allows programmers to make custom modules to extend the functionality without modifying the core of Drupal.
Robustness of its API
Code quality and robustness of its programming interface (API) make Drupal to be also presented as a PHP development environment (Framework). This is called “Content Management Framework”.
How does Drupal?
Drupal is fully programmed in PHP. The set consists of modules revolving around a lightweight core. Each module is somehow a library of functions that enriches and increases application possibilities.
One of the strengths of Drupal is the ability of the modules to interact each other. The downside of this flexibility is the complexity, so often Drupal offers one or more solutions to the same problem. On the other hand, sometimes the hardest part is to find “the” module that best meets your needs.
Another point that distinguishes Drupal from other CMS is that the site and its administration interface are intimately linked: Administrators publish their content in the same graphics context almost as the visitor. This can be confusing at first, but it is this way very productive and intuitive.
Like all CMS, the architecture of a Drupal site based on a specific content model for structuring information. Drupal uses a node system coupled to a particularly flexible taxonomy.
Translated from http://drupalfr.org