All terms
Ground Truth
The verified, correct answer or label that a model's output (or an annotator's label) is measured against.
Ground truth is the reference point everything else is checked against - whether that's a gold response to a prompt, a correctly-drawn bounding box on an image, or a verified fact. Establishing ground truth is usually the highest-trust, best-paid step in a labeling pipeline, since every other judgment depends on it being right.
Example
Before a batch of images is sent out for annotation, a senior reviewer first establishes the ground-truth labels that new annotators' work will be checked against.