system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is a second mortgage and how does it work?

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gpt
A second mortgage is basically a home equity loan.  If you have a mortgage on your house, the home equity is the difference between the value of your house and what remains to be paid in the mortgage.  

For example, if you have a $100,000 house and you still owe $60,000 on it, the home equity is $40,000.  That's the part that's already yours, if you will.

A second mortgage is when you use all or part of that home equity to serve as collateral for a new loan.