Google Publisher Tag (GPT) is an asynchronous JavaScript library provided by Google for web publishers to manage and display ads from Google Ad Manager (formerly DoubleClick for Publishers). This script allows publishers to define ad slots on their pages, specify targeting criteria, and request ads. GPT is designed for high performance, enabling ads to load without blocking the rendering of other content on the page. It supports responsive ad units, custom targeting, line item selection, and robust ad refresh capabilities, ensuring that ads are delivered efficiently and effectively to users based on various parameters. The script acts as an interface between the publisher's website and Google's ad servers, handling the entire ad serving lifecycle from request to display. It helps implement features like single request architecture (SRA) to request multiple ad slots at once, improving page load times and reducing server calls. GPT is essential for publishers utilizing Google Ad Manager to monetize their website content through programmatic advertising.