What does "advance purchase" mean?

What does "advance purchase" mean?

Jen Leo (Daily Deal Blogger, LA Times Travel Section) gives expert video advice on: What are the best ways to book air travel?; What are the different types of air travel websites?; What are some terms to be aware of when booking air travel? and more...

Well, 'advanced purchase' is usually going to give you the best or cheaper fare. So if you book fourteen days in advance or twenty-one days in advance, you are going to get a better deal than if you booked within a week before your departure. This is advanced purchase.