Yellowstone National Park, theYel‧low‧stone Na‧tion‧al Park, the /ˌjeləʊstəʊn ˌnæʃənəl ˈpɑːk $ -ˈpɑːrk/a large national park mostly in Wyoming, in the northwestern US, known for its hot springs and geysers (=natural springs of hot water that rise suddenly into the air), especially one called old faithful which many tourists come to see