Short answer:
A no-deposit bonus is free money or spins you get without adding any cash.
Long answer:
A no-deposit bonus is basically the casino’s way of letting you test the site without taking any risk. You sign up, enter the code if needed, and you get a small amount like a free chip or free spins. You can actually turn this into withdrawable cash, but you’ll need to meet wagering rules first. It’s one of the safest ways to try a casino because you’re not depositing anything upfront.