What is a centerfold?

Newspapers don't have centerfolds. They have double trucks. Technically, the middle two pages of a section (pages 8 and 9 in a 16-page section) is always the double truck, but you don't call it that unless what's on those two pages covers the whole page, or "crosses the gutter" as we say in the biz. A double truck is usually an ad, but it can also be something like pictures of the local high school's graduating class.