Google App Engine is a cloud computing platform that allows developers to build and host web applications without worrying about the underlying infrastructure. It automatically manages the servers, scaling resources up or down based on the application's needs, which helps ensure optimal performance and reliability. With Google App Engine, developers can use various programming languages, such as Python, Java, and Go, to create applications. The platform also provides built-in services like databases, user authentication, and task queues, making it easier to develop and deploy applications quickly and efficiently.