Ground truth

Ground truth is a known, agreed-upon correct answer that you can score against. If the question is "what is 12 times 8?" the ground truth is 96, and grading is mechanical. Many benchmarks rely on ground truth because it makes scoring objective and automatic. The catch is that for open-ended requests, such as "rewrite this paragraph to sound friendlier," there often is no single correct answer, so ground-truth scoring cannot apply. That gap is exactly why human-preference evaluation exists.