@class myClass; //what does this does, I can't figure out :s

Everything is in the title, I doesn't understand what the statement below does:

#import "x.h"
#import "y.h"
#import "MyAppAppDelegate.h"
#import "z.h"


@implementation x

@class myClass;

Could someone explain me using simple words please? I'm quite new to iphone programming :s

Simple Words: It tells the compiler, that there will be a Class named myClass and not to warn you about an unknown class if not really necessary.

Complex Words