Xbox Live key for game what does that mean?

I want to buy a game but cheaper over the Internet than a download key

But it says Xbox one, Xbox Live key

What does that mean?

That I can only play the game if I have Xbox Live Gold?

No, that means you have to redeem it in the console's online store.

However, I would be cautious with key providers. Not all of them are serious.

I often buy using CDkeys that are reputable