It is exactly an arbitrary threshold--defined as 20% down from recent highs. https://www.investopedia.com/terms/b/bearmarket.asp https://www.investopedia.com/t

It is exactly an arbitrary threshold--defined as 20% down from recent highs. https://www.investopedia.com/terms/b/bearmarket.asp https://www.investopedia.com/terms/b/bearmarket.asp EDIT: Adding source.