“On login, wordpress uses the wordpress_[hash] cookie to store your authentication details. It’s use is limited to the admin console area, /wp-admin/
After login, wordpress sets the wordpress_logged_in_[hash] cookie, which indicates when you’re logged in, and who you are, for most interface use.
WordPress also sets a few wp-settings-{time}-[UID] cookies. The number on the end is your individual user ID from the users database table. This is used to customize your view of admin interface, and possibly also the main site interface.”