When someone buys a domain, the domain registrar shows the domain as parked, and most of them show advertising along with the parked domain message. The ads come from Google and many other sites.

Some advertisers don't like their ads appearing on parked domains, because of the lower conversion rate.

By default if you advertise with Google they will show your ads on those parked domains.

More information from Google:
https://adwords.google.com/support/bin/ ... 20onclick=

Information on how you can stop showing your ads on parked domains:
https://adwords.google.com/support/bin/ ... 20onclick=

Thanks for that, ill be sure to use the second link once I start using adsense