A “meltdown” occurs when the stock market suddenly falls by a lot. A “meltup”, by contrast, occurs when money enters the economy so fast that asset prices (stocks markets and property) increase in value very rapidly. Policymakers always want to avoid meltdowns at all costs but are happy to threaten them if or when the public chooses policy options which current policymakers do not like. For example, the economy will “melt down” if the public chooses to exit the European Union.