Gift Letter explained
When a buyer uses gifted money for some or all of their down payment, the lender needs assurance that the funds are truly a gift. A gift letter, signed by the person giving the money, typically states the amount, the relationship between the giver and the buyer, confirmation that repayment is not expected, and that the funds are the giver's own. This protects the lender by confirming the borrower does not have an undisclosed loan adding to their debt obligations.
Gifts most often come from immediate family members, such as parents, and lenders may also ask for proof that the funds have been deposited into the buyer's account. A genuine gift can be a powerful way to boost a down payment, lower the loan-to-value ratio, and improve qualifying numbers, but it must be documented properly to satisfy the lender.