An unknown Korean company registered the word "안드로이드" which is the Korean representation of "Android" as exclusive trademark in Korea, and Samsung negotiated with them and bought (or leased) fully exclusive right for the trademark from them. So other companies can't use the Korean word in their product in Korean market.

Google also registered trademark of the Korean representation for that but only in limited fields, (computing hardware/software), so there was no problem to register the trademark for any another fields (mobile phones, advertising, games communications, internet service, radio, TV …).