Purchase points, also known as a "buy-down" or "discount points," are an up-front fee paid to the lender at closing to buy-down or lower your interest rate over the life of the loan. Each point is equal to one percent of your total loan amount. If you have a $100,000 loan, one point would equal $1,000. The more points you buy, the lower your interest rate, but the more money you'll need at closing.
How do you decide whether you should buy points and if so, how many? Well, the decision should be based on how long you plan on living in your home and what you can afford to pay each month toward your mortgage. If you plan on living in your home for more than five years, it's probably a good idea to purchase points. The longer you live in your home, the more you can save on interest over the life of the loan. But the rates are so low now... I would not.