Galangal is a rhizome of plants in the ginger family Zingiberaceae, with culinary and medicinal uses originating in Indonesia. The rhizomes are used in various Asian cuisines (for example in Thai and Lao tom yum and tom kha gai soups, Vietnamese Huế cuisine (tré) and throughout Indonesian cuisine, for example, in soto). Galangal is related to and resembles ginger. While ginger tastes a little like galangal, most cooks who use both rhizomes would never substitute one for the other and expect the same flavor.
Dictionary source: WordNet 2.0
English to English translation of galangal
Known as laos (Indonesian), lengkuas (Malaysian), kah (Thai), isen, or galingale. It is sometimes called Java root or Siamese ginger. Galangal is a fresh root (a rhizome of a Zinginber species) that resembles fresh ginger root, but has a thinner, translucent, striped skin. Often, it has pink shoots. Its texture is tougher and its flavor is more citrusyand more astringent than ginger. It is always used in cooked dishes and never eaten raw. If you can't find it, ginger is an adequate substitute.