The Threat Advisory System Explained

Bruce Schneier notes that DHS is getting rid of the unloved color-coded "terrorism threat level" system.

I don't remember the last time the threat level changed, but at one point the threat index was lowered to "Elevated", which I found a bit confusing. I wrote the following, lost in my unpublished items until now, which I hope explains the system more clearly:

The terror level has been lowered to elevated. It was high, which is more elevated than elevated, but high isn't as high as the highest level. The highest level is severe, which is the level that is more elevated than high, which in turn isn't the highest level, but is more elevated than elevated and guarded, which is less high than high and elevated, but more elevated than low. Less severe than severe, high, and elevated is guarded, which is higher than low but less elevated than elevated. Low is the lowest. Guarded is more severe than low, but less elevated than severe which is higher than high which is elevated more than elevated which is more elevated than guarded.

Got it?