"Event risk" results from market fluctuations due to real world events, such as the bankruptcy of Lehman Bros., which is usually considered to be the immediate trigger for the financial meltdown last fall. The gasoline price spike that followed the damage inflicted on Gulf Coast refiners by Katrina and Rita is another example, as is bad weather during the growing or harvest seasons  affecting the price of commodities.

As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."

The magnitude of the risk is unknown but bounded by the aggregate of all GDPs and total world wealth. Absent a cataclysmic event such as the perpendicular impact of an asteroid 200km in diameter, the risk for specific events would be some fraction of the above summation.  When applied to markets, the risk is proportional to the investment, but keep in mind that, while you might not own stocks, bonds, commodities or derivatives, your retirement income might depend on them and that the level of regional economic activity determines the ability of regional governments to supply services on which you may depend, including police, fire sanitation, road maintanence, etc.  

As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."