Like AMD's Mantle and the recent complaints about OpenGL and the overhead of OpenGL drivers, Apple has devised its own graphics API that is "closer to metal" and hence its name.
Apple's Craig Federighi said during the presentation that Metal allows for up to 10x the call rates of OpenGL's current speeds while having substantially less overhead. Initially the Metal graphics API is meant for iOS with driving the mobile gaming experience.
Exactly how open the Metal API will be remains to be seen and if/when the Apple Metal API will appear on the desktop within AMD/NVIDIA graphics drivers. At the very least, hopefully all of this recent attention around 3D graphics APIs will lead to faster innovation and growth within OpenGL / OpenGL ES. Metal will premiere later this year with iOS 8 while developers have early access beginning today.
Apple also announced today OS X Yosemite, their latest OS, which will ship later this calendar year.