The Pinterest Tag is a piece of code from Pinterest that an advertiser adds to its website. It lets Pinterest track visitors to the site and the actions they take after seeing or engaging with a Pinterest ad, so the advertiser can measure how well its ads work.
The base code goes on every page of the site. Event codes go only on pages where a specific conversion happens; a conversion is an action such as a page visit, a search, adding an item to the cart, a checkout, a sign-up or a lead. These events appear in conversion reports in Pinterest Ads Manager, build audiences for ad targeting, and are required for conversion campaigns and dynamic retargeting ads, which show ads again to people who visited the site. The tag is installed through an integration partner or by hand, and Pinterest's Conversions API can send the same events from the advertiser's server for more coverage.
The tag requires a Pinterest business account and an advertiser account; it is part of Pinterest's advertising system, where the advertiser pays for ads.