Step 1: Understanding the Concept:
Air movement in poultry houses affects bird health.
The term "air speed" describes this movement.
Step 2: Key Formula or Approach:
No specific formula.
Need to understand poultry house ventilation.
Step 3: Detailed Explanation:
Air speed refers to the movement of air with force.
It is measured in meters per second or feet per minute.
It affects heat loss and ventilation.
Thus, it is air with force.
Step 4: Final Answer:
Air speed refers to air with force.
Hence, the correct option is (D).