What is progressive rendering in HTML?

Progressive Rendering, also known as Progressive Server Side Rendering, is a technique for updating tiny sections of a webpage progressively and streaming it to the client in segments rather than waiting for the full page to be displayed.

It implies that once the important material is produced on the server, you may stream it to the client without having to wait for non-critical stuff to be displayed. It combines the advantages of both CSR (Client Side Rendering) and SSR (Server Side Rendering) (Server Side Rendering).