An image asset catalog is an asset management file type and editor in Xcode 5.
Xcode 5 asset catalogs manage images and icons in multiple resolutions. An asset catalog is a new asset management file type and editor in Xcode 5.
You use asset catalogs to store and manage images for different platforms, devices, and scale factors. The catalog presents the image variants required, and provides you with the ability to define slice and stretch points for images that are resized at runtime.
For more information on Xcode Asset Catalogs, refer here.