Wasabi is a root vegetable that is grated into a green paste. In supermarkets, wasabi is widely available as a paste or in powder form. Wasabi powder has to be mixed with water to become a paste. Wasabi has a strong, hot flavour which dissipates within a few seconds and leaves no burning aftertaste in one's mouth. 

Many "wasabi" powder and paste products that are available in supermarkets (and even some restaurants) contain only very little or no real wasabi at all and are made of coloured horseradish instead. This is due to the fact that cultivation of real wasabi is relatively difficult and expensive.