Final answer:
The white light on an aircraft indicates its tail or rear navigation light, which is crucial for visibility and safety in low visibility conditions.
Step-by-step explanation:
The white light on an aircraft is part of the aircraft's navigation lights, specifically the tail or rear navigation light. This light is used to identify the aircraft's direction when it is viewed from another aircraft or from the ground at night. It helps in preventing collisions by signaling which direction the plane is facing. The light makes the tail of the airplane visible to other pilots and is especially crucial when flying conditions lack visibility such as in darkness or fog.