A home equity line of credit is a form of revolving credit in which your home serves as collateral. Because the home is likely to be a consumer's largest asset, many homeowners use their credit lines only for major items such as education, home improvements, or medical bills and not for day-to-day expenses. A home equity line of credit differs from a conventional home equity loan in that the borrower is not advanced the entire sum up front, but uses a line of credit to borrow sums that total no more than the amount, similar to a credit card.
Another important difference from a conventional loan is that the interest rate on a home equity line of credit is variable based on an index such as prime rate. This means that the interest rate can - and almost certainly will - change over time. The margin is the difference between the prime rate and the interest rate the borrower will actually pay.