You'll never catch me saying I know everything.. At times all system's can and will fail catastrophically and this is why we must all strive to protect our capital first.
The word risk does have a definition..
1. A probability or threat of a damage, injury, liability, loss, or other negative occurrence that is caused by external or internal vulnerabilities, and that may be neutralized through preemptive action.
Read more: http://www.businessdictionary.com/definition/risk.html#ixzz1tvlqex2m
The chart is self explanatory to save me typing here ;)
Click image to enlarge