What does the '^' mean in the code below?

@implementation AppController

- (IBAction) loadComposition:(id)sender
{
    void (^handler)(NSInteger);

    NSOpenPanel *panel = [NSOpenPanel openPanel];

    [panel setAllowedFileTypes:[NSArray arrayWithObjects: @"qtz", nil]];

    handler = ^(NSInteger result) {
        if (result == NSFileHandlingPanelOKButton) {
            NSString *filePath = [[[panel URLs] objectAtIndex:0] path];
            if (![qcView loadCompositionFromFile:filePath]) {
                NSLog(@"Could not load composition");
            }
        }
    };

    [panel beginSheetModalForWindow:qcWindow completionHandler:handler];
}
@end

=== I've searched and searched - is it some sort of particular reference to memory?