WordPress History
WordPress was developed in 2003 by two users of the blogging platform, b2/cafelog, that was being retired by its developers. They developed the new platform based on the discontinued Cafelog but made significant enhancements. For example, there were new templates, a new post editor, and other features. Since 2003, there have been countless new versions of WordPress, each offering additional features and improvements. Some features that have been added along the way were plugins, comment moderation tools, anti-spam featuress, and many more.
WordPress.org Entity
WordPress.org is the open-source platform that allows users to use all sorts of different plugins and create any project they want from scratch. It is a self-hosted platform, meaning users need to find a hosting solution for their site as it is not built-in. The WordPress foundation's goal is to ensure WordPress is always freely available to the public and well maintained/developed.
WordPress.com Entity
WordPress.com is a company that is built based upon the open source WordPress platform. It is not actually directly related to WordPress.org except for having the same name and some similar contributors. This company provides WordPress as a service, including hosting and ease-of-use at the cost of a lack of features and control. Some of the employees of Automattic, WordPress' parent company are regular contributors to the open source platform of WordPress. However, it is important to recognize that these are two completely separate entities that serve two different purposes.
Summary
Wordpress has made leaps and bounds since its conception in 2003 and has gathered a very strong base of users and supporters. It is a universal platform that allows users to manage content on the internet and create any kind of website imaginable.