WordPress powers a very large proportion of the web these days, so in terms of “brand” it’s very strong.
So it’s not that surprising that the WordPress Foundation has formulated a strong, yet clear, trademark policy. Short version – you can’t use the term “wordpress”, but you can use things like “wp”:
Under no circumstances is it permitted to use WordPress or WordCamp as part of a top-level domain name
And this is not an idle statement – they actively defend their position and have and will pursue companies or individuals who infringe their rights.
Here are two recent cases involving three domains:
WordPress Foundation v. Renoo Menard (wordpresswebsitecare.com)
WordPress Foundation v. Karl Delgadillo / Creative Web Design 123 (wordpress-toronto.com,wordpress-support.com)
You could go off and read the decisions, but they’re very straightforward.
Moral of the story – don’t be stupid – WordPress will win the UDRP.