Galangal, also known as blue ginger, is a species of the ginger root. You may not be familiar with the name, but once you smell it you'll know it as the thing that gives many Thai, Malay and Indonesian foods their tang.

I don't think you can get it fresh here (although there is an online website that will ship it to you), so you have to buy the frozen kind. Lotus Supermarket? has some in the freezers, and other shops along the Strip targetted towards Thai or Vietnamese cooking have it in stock as well.