A "busy airport" means that there are many planes taking off, landing, and people moving around, making it a crowded and lively place with a lot of activity. Full definition
I've pumped in extremely busy airport bathrooms with my pump over a hook on the wall using either my battery pack or a nearby plug if there is one available. (rookiemoms.com)
We'd recommend taking the shuttle, to avoid crossing busy airport roads. (holidayextras.co.uk)
It's for this reason we created a colorful slideshow that celebrates the eight busiest airports in the world. (usfunds.com)