Galangal is a close relative to ginger. There are several varieties with the most common are "great galangal" and "lesser galanagal". Lesser galangal roots look like long fingers whereas greater galangal (shown) looks like fresh ginger. Both are use in South East Asian cooking.
Look for fresh galangal in Asian grocery stores. There is a seller on Amazon that ships Fresh Thai galangal. You can substitute dried ground galangal but it is not very good, see substitutes.