If it has anything to do with a similar type of business (advertising) or google's program, it's trademark infringement. Even phonetic spellings can be infringement i.e. (MikeRoweSoft.com - his real name) found this out.
to clarify, you'd be fine depending on how you use it. if you use adwords.org to talk about how to write advertising and nothing on the site is about adwords or google or adsense, there's a very good chance legally you have every right to the domain. but even if you have the legal right to a domain big companies can still push you around and threaten with lawsuits until you give in. google isn't as bad as a lot of others with this though.