Repository vs. Hosting
WordPress.org is a repository site that contains the open-source software for WordPress and makes it available to download for installation on a user’s personal domain. This provides better control and flexibility to the user when building their web site. The user will need to install the software themselves and then rely on their hosting service to provide the appropriate security, spam protection and backups/updates. Some of these functions are available at extra costs. Users will also need to keep up-to-date with the latest software releases from WordPress as updates on their personal web sites will be the user’s responsibility.
In addition to providing the software to download, .org also provides a library of documentation, support forums and training materials.
WordPress.com provides hosting for WordPress and, therefore, does not require the user to purchase a personal domain. Security, spam protection and backups/updates are automatically provided as part of the hosting package. Additionally, updates to the WordPress software will automatically be rolled in without any user interaction. WordPress.com is owned by Automattic and uses the open-source WordPress software.