Hey,
Wavelab=Sound Forge=Cool Edit=Samplitude.
They're all wave editors.
One could argue for days about how one program has this while the other one doesn't....all you need to know is that it is a wave editor, you use it to do some pretty detailed sample-level editing of sounds.
Wavelab used to be amazing when you could run it from within Cubase VST, but now that SX has 'better' wave editing capabilities, they don't allow you to open up external wave editors any more.
You can master just as easily in Cubase now that there are racks which you can load effects into, they all work in real-time. As for detailed sample-level editing, you can do it in SX, but it's not as intuitive and quick as it is in Wavelab (or any other wave editor)
Take care,
Nick