The Google Publisher Tag (GPT) is an ad tagging library provided by Google that allows publishers to define ad inventory, request ads from Google Ad Manager, and display them on their websites. This script handles the communication with Google's ad servers, retrieves relevant ad creatives, and renders them in designated ad slots. GPT supports various ad types and advanced features like responsive design, single request architecture (SRA) for improved page load, and asynchronous ad loading. This script executes in the browser, asynchronously fetching and rendering ads without blocking the page content. It manages ad slot definitions, targeting criteria, and the lifecycle of ad display, ensuring ads are loaded efficiently and comply with publisher-defined rules and privacy settings. It also integrates with other Google advertising services for tracking and optimization.