Other forms: shortfalls
If there's not enough of something, there's a shortfall. You expected to have plenty of Halloween candy, but a shortfall of Skittles has you running to the store to buy more.
When an available quantity doesn't meet your needs, or there's a deficiency of something you want, you've got a shortfall. You might dump out your piggybank and discover a shortfall of cash, or start making a soufflé but find an egg shortfall when you open the fridge. This word comes from the idea of a supply that falls short of expectations.