WordPress is an open-source Content Managed System (or CMS for short), which is a tool for creating all sorts of websites such as online stores and blogs. With an easy user interface, WordPress abstracts away all the complex code like HTML and CSS, allowing anybody with no code experience to build out their own personal page or company website.
Like other popular CMSs like Joomla or Drupal, WordPress was born as an easy way to create a specific form of website, namely blogs. Nowadays, after many years of growth as an open-source system with a rich plugin and themes eco-system, you can build out not only blogs but also personal portfolios, forums, stores, social media, and much more.
Unlike other popular website building tools with custom builder interfaces, anybody can install and manage WordPress websites, which affords you more ownership as the website operator and guarantees you can have a backup of your files as well as the ability to move them from host to host.