I searched for the definition of that term throughout the entire NFPA Fire Codes and found nothing. I did find the following site when I searched via the address line on my browser, and this is what I came up with:
"Temperature Extremes in the United States." Infoplease.com
¬© 2002 Learning Network.
17 Apr. 2002 http://www.infoplease.com/ipa/A0193168.html
I think the term is used by some fire investigators and probably means "not to cold and not to hot?"
My thoughts, when I posted the NFPA 54 reference above was the "source of ignition" that could be present when the electrical equipment and even the electric meter were subjected to some sort of physical damage.
Most gas utilities enforce the 3 foot rule.