An Air Ball in basketball is a shot thrown by a player that does not go through the basket, touch the rim, or even hit the net or the backboard.
It is called such since the ball is floating in the air and missing everything on its path. This shot is usually unblocked.
According to the Oxford English Dictionary, the earliest use of the term Air Ball can be dated back to 1967 in an article from the Daily Review, which states: "Cal State, four times lofting air balls at an orange basket that may as well have been painted invisible."
National Basketball Association Air Ball Moments - [Air Ball][1]
[1]: https://www.youtube.com/watch?v=jG3GwKOHSEM