World knowledge is knowledge about the real world. Humans have implicit knowledge of the real world, but an AI needs to have explicit resources to explain how the real world works. Use this tag for questions about how artificially intelligent systems deal with their need to acquire or apply knowledge about the real world.

Humans know a lot about the real world implicitly.
If someone is said to have "filled their tank", it is implied that they went to a gas station, filled the tank of their car, and paid for it.
An AI does not have this knowledge implicitly; it needs to be taught that this is how things work. It may be taught so explicitly by a teacher or it may learn this from scraping the net, but the knowledge does not come from real-world experiences like humans have.
For this reason, acquiring and applying knowledge about the real world is a field of interest in Artificial Intelligence.