vapour trail 
noun
A trail of condensed water from an aircraft or rocket at high altitude, seen as a white streak against the sky.Down on the lake a boat leaves a rippling wake behind it as it heads towards Wanaka, mirroring the white vapour trail of an airplane that moves silently across a wide blue sky....
- The sky's just the right shade of blue, there's a bird somewhere, and far above, a jet leaves a vapour trail.
- Metadata is the vapour trail we leave behind, not something we construct