There are two types of home equity loans: term, or closed-end home equity loans, and lines of credit (HELOC). Both are usually referred to as second mortgages, because they're secured by your property, just like your original (first) mortgage. Home equity loans and lines of credit are usually for a shorter term than first mortgages.
A closed-end home equity loan, or term loan, is provided to you as a one-time lump sum that is paid off over a set period of time, with a fixed interest rate and equal payments each month. Once you get the money, you cannot borrow further from the loan.
A HELOC works more like a credit card. You are allowed to borrow up to a certain amount over the life of the loan — a time limit set by the lender. During that time, you can withdraw money as you need it. As you pay off the principal, your credit revolves and you can use it again. This gives you more flexibility than a fixed-rate home equity loan.
Credit lines have a variable interest rate that fluctuates over the life of the loan. Payments will vary depending on the interest rate and how much credit you have used. When the life span of a line of credit has expired everything must be paid off. A lender may or may not allow a renewal.
Lines of credit are accessed by specially issued checks or a credit card. Lenders often require you to take an initial advance when you set up the loan, withdraw a minimum amount each time you dip into it, and keep a minimum amount outstanding.