By its very name financial contagion invokes a metaphor, which like all metaphors require an interpretation. In the discussion on financial contagion, key themes emerge and appear in many contexts and this paper follows them. The idea of correlation between or among affected domains - financial instruments, firms, markets, economies, countries, regions, or the world economy is ubiquitous in the analysis of contagion. Economists have long noted that in certain crisis situations, different markets or economies in different countries suddenly start behaving much more similarly than they typically have done. Thus, this sudden increase in correlation of economic behaviour is the prime symptom of contagion.