WKWebView is the centerpiece of the modern WebKit API introduced in iOS 8 & Mac OS X Yosemite. It replaces UIWebView in UIKit and WebView in AppKit, offering a consistent API across the two platforms.

Boasting responsive 60fps scrolling, built-in gestures, streamlined communication between app and webpage, and the same JavaScript engine as Safari, WKWebView is one of the most significant announcements to come out of WWDC 2014.

Mattt Thompson has a handy technical overview of the changes coming to web views (such as webpages opened from your Twitter timeline or an RSS app) in iOS 8. In testing a bunch of iOS 8 apps, I can tell that the difference in terms of performance from iOS 7 is noticeable (and extremely welcome).