An event is an action or occurrence detected by the program that may be handled by the program. The event could be anything like touch event, motion event or remote-control event.
Simply UITouch
also is an part of UIEvent
. UITouch can generate event which is handled by program. Program sense the touch using event.
For more detail information you get in following links, http://developer.apple.com/library/ios/#documentation/EventHandling/Conceptual/EventHandlingiPhoneOS/Introduction/Introduction.html#//apple_ref/doc/uid/TP40009541
http://en.wikipedia.org/wiki/Event_%28computing%29
I hope it will helpful.