A term used in The Legend of Zelda: Phantom Hourglass. It was coined by one of the main characters (Linebeck) and is used as a kind of pet name for Link, the other protagonist of the game. The term was first used in a letter from Linebeck to Link, and has been used by yaoi fan-girls who slash the two characters ever since.
Thanks for working like a dog for me, you Treasure Dog!