Day 21st - Vast.
One of the things I adore in roleplaying games is the vastness of the game world and environments. The details of the vast areas of the game world or universe make for a better roleplaying experience, I find. Even if they are in the background and the players and their characters never get to see the vastness of the game world/universe, they can hear of things happening in the greater world or universe, encounter a variety of people, creatures, and even objects from the greater world. It's a backdrop that, for the most part, enhances the players' and their characters' experience in the game world, by "filling in" the details and gives the game a less than static world feel about it.
That said, while creating fantasy worlds is a lot of fun, the real definition of *vast* can be found in science fiction rpgs that have space as their vastness. The sheer vastness of a rich, large universe offers so much scope and room to play in for GMs and their players and also allows for making part of the black vastness of space "home." And in sf roleplaying games that are based on books, movies, or tv series, the vastness of space allows the GM to do just that, make part of the universe their own for the purpose of telling their own stories in such a game universe. The same applies to homegrown game universes that leave gaps or holes for creative GMs to use and make their own. Such game designs tend to be very creative, for the most part.
Vast doesn't have to be infinite, either... it can be large with limitations imposed on it for reasons of the game designer's choice. But that's a whole 'nother topic for another day...in the vastness of it all...maybe. :)
And there you have this twenty-first post for #RPGaDay for August, 2019. Comments, thoughts, questions, etc. are all welcome, of course.