The Uniform Dispute Resolution Procedure (UDRP) is the system set up by ICANN to resolve disputes between trademark owners and domain name owners. If somebody claims that your domain name violates their trademark, they can choose to initiate the UDRP arbitration procedure instead of suing you in an actual court. This has the advantage of being faster and cheaper for all involved parties, but the disadvantage of being judged in a perfunctory kangaroo court proceeding that sometimes has only a slight passing concern for facts, law, or common sense.
Officially, the complainant in a UDRP proceeding must prove:
(i) the domain name is identical or confusingly similar to a trademark or service mark in which the complainant has rights;
(ii) the registrant of the domain name has no rights or legitimate interests in respect of the domain name; and
(iii) the domain name has been registered and is being used in bad faith.
In actuality, many of the UDRP panelists have been known to make up "bad faith" out of whole cloth, interpret the absence of any use of the domain name at all as "use in bad faith", ignore rights and legitimate interests if the panelist thinks the complainants' rights and interests are more important, and even stretch "identical or confusingly similar" to the breaking point (they ruled "monacogambling.com" to be confusingly similar to "Le Casino de Monte Carlo"). Other panelists, however, have sometimes found for the respondent in similar cases, so it's all up to the luck of the draw whether you get a biased panel or not in your particular case.