Topics they monitor include things like news preferences, topics of interest, and demographics. Based on this information the company collects, they can then show advertising to you they believe will be relevant (I believe it’s on websites that have Adsense enabled). You can opt out of this if you’d like, and I chose to opt out via Chrome plugin.
You might find this interesting if you use Adsense on your websites. By disabling this cookie, you can see what ads would be displayed to the average user who visits your website. For instance, on DogPark.com, the ads now seem more related to dog parks and even dog walking than previously, when I would see web hosting and other technology links.
It’s interesting to see what Google thinks it knows about you, and you can either edit or remove those insights, or you can prevent Google from using the cookie.