Many people only have a "first" mortgage. What does that mean? It means that they only have a single mortgage and it will be the "first" thing to be paid upon sale of the home.

First mortgages normally come with a lower interest rate than any subsequent mortgage. That's because they are more "secure". As with most financial transactions, if the risk to the lender is reduced, the cost to you is reduced. It's the same case with your mortgage. Since first mortgages will be paid first upon sale of the home it is also more likely to be completely repaid than any subsequent mortgage.