The Facebook Pixel gives you the ability to analyse how users interact with your website by tracking specific events on your website. This is important for measuring conversions and the success of your marketing; particularly if you are advertising on the Facebook platform.
The Facebook Pixel collects five types of data:
HTTP headers - Anything present in HTTP headers. HTTP headers are a standard web protocol sent between any browser request and any server on the Internet. HTTP headers include IP addresses, information about the web browser, page location, document, referrer and person using the website.
Pixel-specific data - This includes pixel ID and the cookie.
Button click data - This includes any buttons clicked by site visitors, the labels of those buttons and any pages visited as a result of the button clicks.
Optional values - Developers and marketers can optionally choose to send additional information about the visit through custom data events. Example custom data events are conversion value, page type and more.
Form Field Names - This includes website field names such as "email", "address" and "quantity" when a person purchases a product or service. The pixel does not capture field values unless an advertiser includes them as part of advanced matching or optional values.
In regards to how the information gathered from the Facebook Pixel is used, Facebook states that they:
‘never share information from your website with your competitors or third parties. All information we use is aggregated with millions of other signals before being read by our optimisation systems. Facebook uses information obtained from websites that install pixels to improve its ads. This data is aggregated before it's used.’
You can find out more information on how Facebook’s Privacy and Data Use here