WordPress is easily extended with plugins.

A plugin is an extension to WordPress that adds new functionality.

WordPress is constantly evolving, with new features being added in each new release, and each time a new version of WordPress is released, that functionality is available to you at a very low cost.

The reason that plugins are developed to extend WordPress is because this allows the core WordPress program to be upgraded independently of the addon functionality. This may not seem like a big deal when you first think about it, but without this extensible architecture, upgrades would be much more difficult.

Further, there are thousands of existing, free plugins available for WordPress. This means that you can often add a feature with one click that would otherwise represent thousands of hours of coding if that feature needed to be developed from scratch.