The two main components of any home loan are the “promissory note” and the “deed of trust.”
The promissory note is essentially a contract that contains a pledge to repay the loan amount and the terms for repayment (which includes interest rate, loan term, loan amount, etc).
The deed of trust – also called a “mortgage” or “lien” – states that the home may be used as “collateral” for repayment of the loan; in the event of payment default, the lender is able to foreclose on the property, sell it, and retain the proceeds to satisfy the debt in question.
Every lien has a “position” or “priority.” All home loans have at least one position – “first position.” The lender in first position gets the first crack at recouping its losses in the event of payment default.
It is possible for borrowers to take out additional liens (mortgages) on a home. All subsequent liens are “subordinate“, which means that the lender in secondary position must wait to be made whole until after the first is finished. You might also see this referred to as a “second lien“, a “second mortgage“, or a loan in “junior position.”