The Google Publisher Tag (GPT) is an ad tagging library provided by Google that enables publishers to implement programmatic advertising on their websites. It's loaded asynchronously in the browser and is responsible for communicating with Google's ad servers to fetch relevant ad creatives based on defined ad slots, targeting criteria, and user consent status. GPT handles the display of these ads, manages their lifecycle, and integrates with features like header bidding and audience solutions. It helps publishers maximize ad revenue by efficiently delivering ads while adhering to various ad policies and technical specifications. The script operates client-side, making requests to Google's ad infrastructure to retrieve ad content and report ad impressions and clicks. It often works in conjunction with other Google services to ensure ad relevance, frequency capping, and brand safety for advertisers and publishers.