For example, if you own a home worth $300,000 and sell it to a family member for $200,000, they've received a gift of equity of $100,000. A gift of equity can occur if a home is given away for no compensation or if a discount is offered on its value.
Conventional lenders won't accept gifted equity as a downpayment. Heck, almost no commercial lenders will allow it either. The concept of collateral is really lost at that point.