"left luggage"

"Left luggage and lockers are available in both terminals"
what does "left luggage" mean?

Sounds strange to me but maybe they mean forgotten luggage, although it doesn't make much sense.

For sure it's a place where you can leave your luggage for some time for money. E.g. your plane depart for two hours and you want to take a look around the airport, so you won't walk with all your cases and bags, just leave it in a 'left luggage' room/office for money, and they take a look of it.