What are progressive web apps (PWA)? Before defining that, understand that they are not the same as single page apps.

• Reliable – Load instantly and never show the downasaur, even in uncertain network conditions.
• Fast – Respond quickly to user interactions with silky smooth animations and no janky scrolling.
• Engaging – Feels like a natural app on the device, with an immersive user experience.

There is a good YouTube video on this topic called Progressive Web Apps (PWA) Tutorial for Beginners – Getting Started. This video on YouTube is the entire first section of a course at Udemy.com. There is another video by the same author at YouTube called Building Our First PWA | Example Project.