Horseradish is the gnarled, long, creamy coloured root which often translates as 'pepper root' in other languages. This is not a misnomer as it bears a swingeing heat. Hugh Fearnley Whittingstall describes the flavour thus 'shades of peppermint and waves of mustard.' It looks pretty harmless until you get at it to do things with it. If cutting onions causes you to weep then dealing with horseradish will send you to Hades. "The heat comes from sinigrin, a volatile, pungent compound similar to mustard oil in its intensity and effect". I hope this is not entirely true as mustard oil is now virtually banned in Bengal, where it has traditionally been a staple of the diet, because of other less attractive properties.
It is easy to grow but has a tendency to proliferate at the expense of its neighbours. Again, Hugh Fearnley Whittingstall makes a useful comment here. Store freshly-lifted roots in a bucket of sand and they will keep for months. Or, alternatively, they will keep in the salad drawer of the fridge for a couple of weeks. He also says that it freezes well, like ginger, grated straight from its frozen condition.
It is one of the five bitter herbs essential to the Seder, the Passover meal of the Jewish community.