### Instruction:
What does airplane glide ratio mean?

### Response:
Airplane glide ratio is a measure of an airplane's glide performance. It is the ratio between distance forward to distance downward for an airplane in free, unpowered flight. Glide ratio is affected by properties such as aerodynamical drag, wing construction, and more. Sailplanes are among the most efficient airplanes, achieving glide ratios over 70:1.