The "forward slip" thing is a US term.
There was a lengthy discussion on it in this
thread some time ago.
If you go to the FAA website and have a look at some of the documents there (I gave some references in the above thread) all will be revealed ... but I still can't see what the difference is between the "forward slip" and the good old garden variety sideslip ... other than the picture outside the cockpit. Does that mean I am a dinosaur tried and true ?