We have seen multiple applications using WYSIWYG.Eg: MS office applications, Adobe Photoshop, Illustrator and so on. Recently I came across Miro and started using it extensively. What does the Layout of Miro called ? Like we term the Photoshop ones as WYSIWYG.
I think the words you're looking for here are infinite canvas and perhaps pageless. Word, Photoshop et al. all are operating on the assumption that you are putting content on a page which one day ends up being printed, or otherwise confined to a pre-determined size. Tools like Miro, Figma and "whiteboard applications" in general on the other hand don't really want you to print out what you're doing in them, rather their entire thing is to give you as much room as you need to organize your ideas.
In terms of GUI (Graphical User Interface) patterns, Miro pattern is a virtual whiteboard, where users can interact with the digital canvas and its elements using familiar metaphors from physical whiteboards and sticky notes. It is very user-friendly, and allows multiple users to contribute simultaneously, regardless of their location.
While I like to call it "virtual mood board" (which is applicable to describe how we use it in our company), the broader and more accurate classification for Miro is as a "collaborative online whiteboard" (which in time is a version of Interactive Whiteboards) application. It's essentially a digital workspace that enables real-time collaboration and visualization of ideas, and of course it includes Miro, but also FigJam, Invision, Mural, Google Jamboard and Ziteboard just to mention the most known.
The idea, as Leo Wattenberg correctly said, is that space is virtually infinite and you can have literally thousands of collaborators sharing ideas without space limitations. As an example, my daughter uses it in university and there are hundreds of students posting their work (which usually have lots of pieces, up to 100) and the professors can share immediate feedback, same as the students between them.