Thanks - I always get those two bollixed up.
To me, "retarding" the timing means firing it later, while "advancing" the timing makes it fire earlier. You'd fire it earlier to get your P-V curve back if you're detonating, and you usually work to fire a bit later than stock to improve the P-V-theta timing (peak pressure resulting in increasing volume at 12*ATDC, to maximise leverage on the crankpin.)