It was coined in 2011, and is based around the fact that Waffle House in an extremely resilient restaurant chain. The restaurant will usually be open during extreme weather, or reopen quickly if they’re forced to close down. As a result, the Federal Emergency Management Agency (FEMA) has developed an informal "Waffle House" index that measures how severe an emergency was.
There are three levels: Green, Yellow and Red. Green means that the restaurant is operating at full capacity. Yellow, that there is a restricted menu, indicating loss of power or food supplies. Red, the restaurant is closed. It's been said that Waffle House is one of few really good examples of disaster planning and preparedness. They prepare and plan for disasters, so the index rarely ever gets down to red.