What does « Dog » mean in the Quran?

They ask you, [O Muhammad], what has been made lawful for them. Say, "Lawful for you are [all] good foods and [game caught by] what you have trained of hunting animals which you train as Allah has taught you. So eat of what they catch for you, and mention the name of Allah upon it, and fear Allah." Indeed, Allah is swift in account.

And if We had willed, we could have elevated him thereby, but he adhered [instead] to the earth and followed his own desire. So his example is like that of the dog: if you chase him, he pants, or if you leave him, he [still] pants. That is the example of the people who denied Our signs. So relate the stories that perhaps they will give thought.

And you would think them awake, while they were asleep. And We turned them to the right and to the left, while their dog stretched his forelegs at the entrance. If you had looked at them, you would have turned from them in flight and been filled by them with terror.

They will say there were three, the fourth of them being their dog; and they will say there were five, the sixth of them being their dog - guessing at the unseen; and they will say there were seven, and the eighth of them was their dog. Say, [O Muhammad], "My Lord is most knowing of their number. None knows them except a few. So do not argue about them except with an obvious argument and do not inquire about them among [the speculators] from anyone."