This has nothing to do with copyright. And everything to do with trademark law. Most people often confuse a copyright with a trademark. I won't go into the details between the both, just read up on it.
But if the term is trademarked. And you want to use that term in a simular industrial reference and for profit, then you risk getting sued by the trademark holder. Using your example, if your site is in reference to Audi or it's industry in any way, they will sue you. Because you are technically diluting their trademark. The trademark protects the holder from having any confusion with it's brand and identity.
Now technically, you could use another companies trademark term if you use it in a fashion that there is absolutely no confusion between you and the trademark company.
Example, Audi has the trademark of TurboFSI. But if you open a business and offer TurboFSI flip flops. You could get a TurboFSI trademark under a shoe wear classification. Something that has nothing to do or as far away as Audi's car related classification. There simply must not be any confusion between to two companies or products.
Now, that is technically. Can Audi still sue you? You bet your ass they can. Because as I've posted here before. The company who has the gold makes the rules. Audi can sue your ass to kingdom come. Keep you in the courts for years, and bleed you dry until you go out of business.
So, I wouldn't even bother with a trademarked name. Now I understand that you could use a trademarked name if you don't profit from it. For example, TurboFSIsucks.com or PayPalSucks.com. You can have a forum on how you don't like or like their prouduct. But you can't make a dime on it. So again, it's not even worth it. Best advise talk to a trademark lawyer if you still want to pursue this.
Good luck.