When it comes to credit cards, your APR is another term for your interest rate. If a credit card offers a 0% intro APR on balance transfers, that means for a certain period of time, you can transfer debt to it and accrue no interest.
You’ll have to make at least the minimum monthly payment even though no interest is accruing, however. And once the intro APR ends, you’ll start accruing interest at the regular APR on any balance that remains.