I don't see the necessity of having a catch-all word. Why not say "delete" when you mean delete, and "erase" when you mean erase? Both words are absolutely standard and well-known. And anyway, why bother to delete anything when you can erase it?. Your answer is evasive and confusing, and has confirmed my intention of having nothing to do with CCleaner.
I cannot find anywhere a definition or description of what "clean" means in this context, and I find that unusual and suspicious. Basically it might mean "delete" or "erase", both terms being well-known and understood. I would hope it means "erase" - that is the destruction of the data so that it cannot be recovered but in that case one would expect at least a brief description of the process used. I would certainly not buy any software which omitted this basic information.