What is "Worldbuilding?" 

"1. What we mean when we say 'Worldbuilding'

We’re talking about the revelation of your storyworld and its details through the story itself. It’s easy to think this means “setting,” but that’s way too simple — worldbuilding covers everything and anything inside that world. Money, clothing, territorial boundaries, tribal customs, building materials, imports and exports, transportation, sex, food, the various types of monkeys people possess, whether the world does or does not contain Satanic “twerking” rites."
-Chuck Wendig
Worldbuilding is the process of constructing an imaginary world, sometimes associated with a whole fictional universe. The term "worldbuilding" was popularized at science fiction writers' workshops in the 1970s. Developing an imaginary setting with coherent qualities such as a history, geography, and ecology is a key task for many science fiction or fantasy writers. Worldbuilding often involves the creation of maps, a backstory, and people for the world. Constructed worlds can enrich the backstory and history of fictional works, and it is not uncommon for authors to revise their constructed worlds while completing its associated work.
-Wikipedia
Adapted from: "Worldbuilding"