Wasabi is Japanese horse-radish.

It is most famous when served as green paste with Japanese sushi.   

Wasabi come from the root of an asian vegetable.  The root is ground into a green paste, which then becomes wasabi.

Wasabi has a strong, hot flavour.  The spicy flavour disappears in only a few seconds and leaves no burning after taste in your mouth.

In supermarkets, wasabi is often sold as a paste or in a powder form.  Wasabi powder has to be mixed with water to become a paste.  These supermarket products contain very little or no real wasabi.  This is because that the farming of real wasabi is difficult and expensive.