X11 is the traditional most popular display server for Linux and other *nix systems. However it is very dated and has a lot of flaws, including endless spaghetti code that makes maintenance a nightmare, huge security holes where any application can freely scrape information from any other, and tons of bugs dating back decades. It isn’t sustainable to keep developing on X11 as a platform because it is so flawed and devs hate working on it when implementing new features or fixes.
Wayland is a modern protocol for display server/compositing tasks which seeks to directly address all of the major issues of X11. It is small and modular, with purpose driven portals and protocols written to interact with a simple core, rather than being monolithic and opaque like X11s code structure. It is security focused, with the aforementioned portals used to grant permissions to applications when needed but nothing more. Wayland has a more efficient pipeline resulting in better performance. It is overall a pleasure to work on comparatively and is a much richer, progress oriented protocol than X
Why are you hearing about it now? Because Wayland is finally mature enough to warrant almost everybody to stop using X11. There are a few features that are still not present in Wayland that should be for particular use cases, but these are exceptions nowadays. Applications are starting to prioritize Wayland compatibility, distros have overwhelmingly made the switch to it as default, and most Linux display server developers have moved away from X and onto Wayland. It seems that the transition is nearly complete but the last hurdles have certainly been creating lots of discussion