That said, WordPress.com and WordPress are not interchangeable terms. WordPress.com is distinctly Automattic's product and not in any way related to the open source project.
WordPress is a content management system that is open source and developed by hundreds of contributors that volunteer their time and efforts. Many of those contributors work for companies that utilize WordPress in their day to day.
Automattic is one of the companies that supports some of their employees to work on the WordPress project, however they have no official ownership of the project.
How to distinguish WordPress versus Automattic
When a blogger or journalist references WordPress, WordPress.com, and Automattic, it is important to be specific in how you identify each entity.
- Automattic owns and runs WordPress.com, but WordPress.com is only one of their products.
- WordPress.com runs on WordPress, but the two terms are not interchangeable (The .com is important to include when referencing it).
- WordPress is open source and no corporate entity runs it or is parent to the project.
- The WordPress Foundation manages the trademark for WordPress.
- The trademark is typically not allowed to be used, but WordPress.com has an exception.
- Matt Mullenweg is a co-founder of WordPress, the founder of Automattic, and the head of the WordPress Foundation. Yes, this is confusing, but the differences matter.
Why does it matter how WordPress / WordPress.com / Automattic are referenced?
Primarily, it's important because many people misattribute the WordPress project to Automattic, the company.
The people that work on WordPress put their energy and passion into the project. It's demoralizing to hear the project referenced as something made by a company you have nothing to do with.
If you ever write about WordPress and are looking for a way to reference it, be sure you're denoting the project properly. WordPress is an open source content management system.