The intention is to display ads that are relevant and engaging for the individual user and thereby more valuable for publishers and third party advertisers.</p> Name Provider Purpose Expiry Type _fbp Facebook Used by Facebook to deliver a series of advertisement products such as real time bidding from third party advertisers. 3 months HTTP Cookie _gcl_au Google Tag Manager Used by Google AdSense for experimenting with advertisement efficiency across websites using their services. 3 months HTTP Cookie _rdt_uuid Reddit Used to track visitors on multiple websites, in order to present relevant advertisement based on the visitor's preferences.