For most people, UGGs are warm, slightly odd shaped boots, usually made from sheepskin.
For Deckers Outdoor Corporation, also offering Teva sandals, it is a billion dollar business under the umbrella of a broadly diversified brand.
Deckers bought the trademark UGG Australia from an Australian in California. And made product and trademark famous in ~130 countries, where it owns trademarks.
Except for Australia, where the boots originated and Ugg is the generic term.
One Australian manufacturer is fighting Deckers through the American court system. He wants to sell his boots as Uggs in the USA.
According to the NYT he has only one more shot at the highest court.