Google Publisher Tag (GPT) is an ad tagging library provided by Google that allows publishers to define ad slots on their webpages and request ads from Google Ad Manager. When a webpage loads with GPT, the library builds a request for ads based on the defined ad slots, targeting criteria, and user context. It then communicates with Google's ad servers to fetch and display the appropriate advertisements. The script handles ad rendering, refresh, and responsiveness, ensuring ads are displayed correctly across various devices and screen sizes. GPT optimizes ad delivery by supporting features like asynchronous ad loading, single request architecture (SRA) to request multiple ad slots simultaneously, and lazy loading. It also facilitates programmatic advertising by integrating with Google's ad exchange. This script is crucial for websites that monetize through Google Ad Manager, providing the infrastructure for displaying targeted and relevant ads to users.