To be bug free we must be able to define what a bug is. So, what is a bug?
The reason for that quote is from what you have said a bug would be anything you didn't expect, even if it is consistent or not with the specification as that merely affects if we classify it as functional or not (a classification I profoundly disagree with, obviously). It is simply a negative rephrasing of what the marketing guy said and laughable in the same way.
> One plausible definition is “system deviates from its specification”
And that's quite reasonable. So I actually retract my argument.
For my own definition, I was considering a bug to be any behavior that the software engineers weren't expecting. Because those can exist invisibly for a long time until they become so bad they become visible. They can also exist for decades without causing any problems to functionality at all.
The reason for that quote is from what you have said a bug would be anything you didn't expect, even if it is consistent or not with the specification as that merely affects if we classify it as functional or not (a classification I profoundly disagree with, obviously). It is simply a negative rephrasing of what the marketing guy said and laughable in the same way.