The Google Publisher Tag (GPT) is a client-side JavaScript library that allows publishers to define and manage ad slots on their webpages and to make ad requests to Google Ad Manager. When a webpage loads with GPT, it communicates with Google's ad servers to fetch relevant advertisements based on various criteria, including user demographics, page content, and ad targeting rules set by the publisher. GPT handles the rendering of these ads within the designated ad slots, ensuring that ads are displayed correctly and efficiently. It supports various ad formats, responsive design, and advanced targeting capabilities, enabling publishers to maximize their ad revenue. GPT is designed to be asynchronous, meaning it doesn't block the loading of other content on the page, contributing to a better user experience. It also provides features for controlling ad refresh rates and managing user consent for personalized advertising, which is crucial for global privacy compliance regulations like GDPR and CCPA.