One of the mysteries of the English language finally explained.
Definition of ground-truth in English:
ground-truth
verb
with object To confirm or validate directly (information or data derived indirectly), especially (in remote sensing) by direct observation on the ground, rather than by interpretation of remotely obtained data; to make observations of (land, an area, etc.) directly on the ground, especially in order to confirm or validate data obtained indirectly.
Origin
1980s; earliest use found in American Antiquities. From ground truth.