Progressive Web Apps (PWAs) are a type of web application built with standard technologies like HTML, CSS, and JavaScript, designed to combine the best features of the web and native mobile apps. They follow a principle of progressive enhancement, providing a baseline website experience to all users while offering advanced, app-like capabilities on supported browsers and devices. Key features, powered by technologies such as service workers for offline caching and a web app manifest for installation details, include offline functionality, push notifications, and the ability to be installed on a user's home screen, creating a fast, reliable, and engaging experience that blurs the line between a website and a traditional application.