Apple reviews every app submitted to the App Store. New apps and updated apps.
That takes time. Sometimes a long time.
The Apple Developer Support portal tries to clear up things a bit. First you learn about the App Store guidelines. What Apple thinks as a great app. Why app make it or not on the App Store.
Apple App Store App Review Status Information
Apple provides information for app submissions reviewed in the last 5 business days.
As of September 12, 2014 only 35% of new iOS apps and 53% of iOS app updates have been reviewed.
Looks like the release of iOS 8 is slowing things down. A lot.
You need an Apple developer account to login to the Apple Developer Support portal.