WordPress is a free and open-source content management system based on PHP & MySQL. Features include a plugin architecture and a template system. It is most associated with blogging but supports other types of web content including more traditional mailing lists and forums, media galleries, and online stores.
“WordPress is a factory that makes webpages”
WordPress users may install and switch among different themes. Themes allow users to change the look and functionality of a WordPress website without altering the core code or site content. Every WordPress website requires at least one theme to be present and every theme should be designed using WordPress standards with structured PHP, valid HTML (HyperText Markup Language), and Cascading Style Sheets (CSS). Themes may be directly installed using the WordPress “Appearance” administration tool in the dashboard, or theme folders may be copied directly into the themes directory, for example via FTP. The PHP, HTML and CSS found in themes can be directly modified to alter theme behavior, or a theme can be a “child” theme which inherits settings from another theme and selectively overrides features. WordPress themes are generally classified into two categories: free and premium. Many free themes are listed in the WordPress theme directory, and premium themes are available for purchase from marketplaces and individual WordPress developers. WordPress users may also create and develop their own custom themes. The free theme Underscores created by the WordPress developers has become a popular basis for new themes.
WordPress’ plugin architecture allows users to extend the features and functionality of a website or blog. As of June 2019, WordPress.org has 55,131 plugins available each of which offers custom functions and features enabling users to tailor their sites to their specific needs. However, this does not include the premium plugins that are available (approximately 1,500+), which may not be listed in the WordPress.org repository. These customizations range from search engine optimization, to client portals used to display private information to logged in users, to content management systems, to content displaying features, such as the addition of widgets and navigation bars. Not all available plugins are always abreast with the upgrades and as a result they may not function properly or may not function at all. Most plugins are available through WordPress themselves, either via downloading them and installing the files manually via FTP or through the WordPress dashboard. However, many third parties offer plugins through their own websites, many of which are paid packages.
Web developers who wish to develop plugins need to learn WordPress’ hook system which consists of over 300 hooks divided into two categories: action hooks and filter hooks.
Information Source : Wikipedia