When you mortgage a property that means that you offer the property as collateral for a loan.

当你通过抵押贷款购买一项财产意味着,你需要抵押这项财产的所有权以获得贷款

耶鲁公开课 - 金融市场课程节选

There are lots of costs, so you want to have a loan-to-value ratio, which is sufficiently low, that the collateral will cover the value of the loan.

那是一大笔开销,因此你要设定一个足够低的,贷款价值比率,使得抵押物价值能够为贷款提供保障

耶鲁公开课 - 金融市场课程节选