Worldbuilding is the process of creating fictional worlds for books, games, tv show and similar. It includes the big stuff, such as maps, planets, nations, civilizations, gods and heroes and subtle things such as architecture, costumes and what people eat.
For speculative fiction, worldbuilding is generally an important if not critical part of what makes them work. Indeed many people get into works of fiction because of the worlds built for them and look out for series with good worldbuilding in it. Never the less it is only one part of what's required to make an good story. There is a reason why The Lord of the Rings (an actual story about people caught up in events involving hobbits, elves, orcs, rings, a dark lord, etc) has outsold the Silmarillion (a History of Arda). Worldbuilding on it's own is like reading a history book, engaging to those who are into that but also dry.
Traditional Games can get away with an abnormally high worldbuilding to everything else content since what they are selling is not a story as much as a framework for stories which other people make as they go.
Settings with Good Worldbuilding
- Middle Earth
- Avatar: The Last Airbender
- The Stormlight Archives
- Thomas the Tank Engine - (We're not Kidding)