Short answer: A letter proving family money is a gift, not a loan. Required by banks for deposit gifts.
If family gives you money for your deposit, the bank needs a letter proving it is a gift, not a loan. A gift does not need to be repaid. A loan would count as debt and reduce how much you can borrow. The letter must say the money is unconditional and does not need repayment.
Giver: Parent
Amount: $20,000
Statement: This is an unconditional gift. No repayment required.
Bank Requirement: Signed and dated by giver