This is the 3903rd most frequent Russian word.
воздушные
"Air," "aerial," or "airy," depending on the context.
Here, 'воздушные' means 'air' or 'filled with air,' describing the balloons.
Воздушные шары поднимаются в небо.
The balloons are rising into the sky.
In this context, 'воздушные' is metaphorical, referring to something fanciful or unattainable (castles in the air).
Он создает невероятные воздушные замки в своем воображении.
He builds incredible castles in the air in his imagination.
In this sentence, 'воздушные' describes the pastries as light and fluffy in texture.