About this cookie:
Used by various facebook features for logged in users
About this cookie’s host: This domain is owned by Facebook, which is the world's largest social networking service. As a third party host provider, it mostly collects data on the interests of users via widgets such as the 'Like' button found on many websites. This is used to serve targeted advertising to its users when logged into its services. In 2014 it also started serving up behaviourally targeted advertising on other websites, similar to most dedicated online marketing companies.
Related general information about p:
These cookies are used to deliver adverts more relevant to you and your interests. They are also used to limit the number of times you see an advertisement as well as help measure the effectiveness of the advertising campaign. They are usually placed by advertising networks with the website operator's permission. They remember that you have visited a website and this information is shared with other organisations such as advertisers. Quite often targeting or advertising cookies will be linked to site functionality provided by the other organisation.
More about cookie classifications
Third Party Cookies
If the host domain for a cookie is different to the one in the browser bar when it was downloaded, then it is a third party cookie.
They are usually placed in a website via scripts or tags added into the web page. Sometimes these scripts will also bring additional functionality to the site, such as enabling content to be shared via social networks.
For example, if you visit a site that has a YouTube video in one of its pages. This has been included by the website owner, using a piece of code provided by YouTube. YouTube will then be able to set cookies through this code, and know that you have watched that video, or even just visited the page the video is in.
Online advertising is the most common use of third party cookies. By adding their tags to a page, which may or may not display adverts, advertisers can track a user (or their device) across many of the websites they visit.
This allows them to build up a 'behavioural profile' of the user, which can then be used to target them with online ads based around their 'calculated' interests.
Session Cookies are only stored temporarily in the browser's memory, and are destroyed when it is closed down, although they will survive navigating away from the website they came from.
If you have to login to a website every time you open your browser and visit it - then it is using a session cookie to store your login credentials.
Many websites use session cookies for essential site functions, and to make sure pages are sent to the browser as quickly and efficiently as possible.