Is iPad a multi-tasking device?
iOS devices could always play play audio in the background. From iOS 4, 3rd party apps may also run in the background, but the multitasking ability is restricted. Applications which aren't running are frozen to save CPU and battery life. However there are 7 background API's which may execute in the background : 


Background audio
Voice over IP
Background location
Push notifications
Local notifications
Task finishing
Fast app switching


See here for more info: http://en.wikipedia.org/wiki/IOS_(Apple)#Multitasking