These are set by Automattic and trusted third party networks, and are generally persistent in nature. Third Party / Embedded Content Sites hosted on WordPress.com make use of different third party applications and services to enhance the experience of website visitors. These include social media platforms such as Facebook and Twitter (through the use of sharing buttons), or embedded content from Youtube and Vimeo. As a result, cookies may be set by these third parties, and used by them to track your online activity.