Wasabi (known by the names Wasabia japonica or Eutrema japonica, as well as others) is plant that is a member of the Cruciferae or mustard family. Commonly known as Japanese horseradish, it grows naturally along stream beds in mountain river valleys in Japan. It is green, and extremely strong flavored. Its hotness is different from chili pepper, which burns the tongue; wasabi's strong sensations shoot up one's sinus cavity instead.
It is sold either in root form, as a dried powder which is then mixed with water to make a paste, or as a ready-to-use paste, which comes in tubes approximately the size and shape of travel toothpaste tubes.
Fortunately for those who either through malice or unfamiliarity come into contact with too much of this condiment, the burning sensations it can induce are short-lived compared to the effects of chilis. When used as intended, it is also very tasty on roasted peas, or in small amounts on sushi or sashimi. Wasabi is commonly mixed with soy sauce to make a dipping sauce for sushi and sashimi.
Most of the "wasabi" served today is really just horseradish dyed green, or a mix of horseradish with mustard and chlorophyll for the same effect. The demand for real wasabi is very high. The state of Oregon is one of the world's top producers of this condiment.
