I think that in some circles the term 'forward slip' is now applied to what used to be called 'side slip', ie the aircraft tracks a straight line over the ground, usually the approach centreline. In these circles, 'side slip' has become slipping laterally across the ground, starting to one side of the extended centreline but arriving over the runway on the centreline, assisted where possible by any crosswind.
From Handling the Big Jets , by Dai 'The Book' Davies, ARB Chief Test Pilot: "It is wrong in principle to allow a swept wing aeroplane to suffer significant angles of sideslip". Good enough for me, except, as mentioned earlier, when faced with a no-thrust approach.