A first trust deed is a type of loan that has the first priority lien on a property, which means that it is the first loan to be paid off in the event of a default or foreclosure. This makes it less risky for lenders and generally offers lower interest rates for borrowers.

A second trust deed, also known as a junior lien or second mortgage, is a loan that is subordinate to the first trust deed. This means that it has a lower priority in terms of repayment in the event of default or foreclosure. Because second trust deeds carry a higher risk for lenders, they often come with higher interest rates than first trust deeds.

In a real estate transaction, a first trust deed is typically the primary mortgage used to finance the purchase of a property, while a second trust deed is used to borrow against the equity in a property or to provide additional financing for a property that already has a first trust deed in place.