Wasabi is a popular Japanese spice known for its great heat. It is made from the root of the wasabi plant and is commonly used to flavor sushi. The spice is very widely used in the USA but it turns out it is really challenging to find real wasabi in the States.
Most of the Japanese spice consumed in the USA is fake wasabi made of mustard, horseradish and coloring agents that produce the greenish nuance of the condiment. The mixture of mustard and horseradish actually has the similar heat of the real spice but it doesn’t have its complex flavors it is famous for.
So, this means that most probably you often eat fake wasabi when you visit sushi restaurants, even if it is sold at the price of the genuine spice. It is really hard to find actual wasabi in the USA, so you may have to go to Japan in order to enjoy it.