What is Trademark Clearinghouse?

Legal Definition
The Trademark Clearinghouse is a database of validated and registered trademarks established by ICANN to assist trademark holders prevent infringing behavior in the Domain Name System. In combination with the Uniform Rapid Suspension System (URS), it is the second significant attempt by ICANN to handle the "Trademark Dilemma". The first attempt was the Uniform Domain-Name Dispute-Resolution Policy.

The Trademark Clearinghouse is not a trademark office. Rights holders who register their marks with the Trademark Clearinghouse must still register with their country's trademark office. The primary purpose of the Trademark Clearinghouse is to maintain a global database of verified trademarks for the Domain Name System.

The Trademark Clearinghouse is strictly for Second-level domain names. Other mechanisms exist to protect trademark in the new gTLDs themselves. All new gTLD registries are required to use the Trademark Clearinghouse and URS for protection of Second-level domains.
-- Wikipedia