Modules
As we discussed in Chapter 1, Introduction, Drupal is highly modular in its design; you can switch on or off various bits of functionality by enabling/disabling modules, and you can also extend the system by adding new ones.
Other systems may describe modules as plugins—the two are synonymous.
Core and contrib modules
The term Drupal core refers to the set of modules that are present in the main Drupal download that you have just installed. You can achieve a great deal using just these, but developers around the world have created their own modules for specific areas of functionality, which you can also use free of charge.
Collectively, these community-contributed modules are referred to as contrib modules.
All modules can be downloaded from the Drupal website (https://www.drupal.org), and each one has its own individual project page. The project page for each module contains the downloadable code, releases, documentation, and links to the issue queue that we will discuss later...
