I was going through iOS Human Interface Guidelines.
It was mentioned as
Display a launch image that closely resembles the first screen of the application. This practice decrease the perceived launch time of your application.
Avoid displaying an About Window or a splash screen. In general, try to avoid providing any type of startup experience that prevents people from using your application immediately.
What is the difference between a launch image and a splash screen?
Launch Image may take a little short time. It shows when app loading starts into iphone volatile memory. it shows for very short.
Splash screen means, that you display an Image until your necessary information loading not complete. Like, U can see any loading image before start any heavy game. When all data loading complete then this screen removed and game statrs. It may shows for little long. !