Google Publisher Tag (GPT) is a JavaScript library provided by Google Ad Manager that allows web publishers to define ad slots on their pages and request ads from Google Ad Manager. It dynamically builds ad requests, handles ad rendering, and integrates with Google's ad serving infrastructure. The script ensures that ads are loaded asynchronously, improving page load performance, and supports advanced features like responsive ads, targeting, and frequency capping. When the script executes, it communicates with Google's ad servers to fetch relevant ad creatives based on defined targeting criteria (e.g., user demographics, page content, device type) and renders them within the designated ad slots on the webpage. It is a critical component for publishers monetizing their content through Google's advertising ecosystem. GPT loads ads in an iframe for security and isolation, preventing ads from interfering with the main page content. It manages ad inventory, ensuring proper ad rotation and delivery according to publisher and advertiser settings. It also collects data related to ad impressions and clicks, which is used for reporting and billing within Google Ad Manager. The script is designed to be highly flexible, allowing publishers to implement complex ad layouts and behaviors.