ground truth
n.— «Weather spotters provide what’s called “ground truth” to the National Weather Service and emergency weather management. “We’re needed because cloud-piercing Doppler radar is very good at helping the National Weather Service see what’s going on in the upper atmosphere, but it’s unable to detect what’s actually happening on the ground because of the curvature of the Earth.”» —“Volunteers track storms” by Debra Carr-Elsing Capital Times (Madison, Wisconsin) Oct. 26, 2006. (source: Double-Tongued Dictionary)
Further reading
Sara in Madison, Wisconsin, was reading an old edition of The Joy of Cooking and came across a recipe that described a cake’s ingredients as earrings for an elephant. She couldn’t discern whether the authors meant that was a good thing...
Astronauts returning from space say they experience what’s called the overview effect, a new understanding of the fragility of our planet and our need to reflect on what humans all share as a species. A book about the end of the universe...