Safety gap

Hi to all:
I'm a little new at this, and I did not use one on my first coil. So would 
someone please explain in laymen's terms what a "safety gap" is, and how it 
is incorporated into the primary circuit of a Tesla coil? I know what a spark 
gap is, and how it works, but I'm not familiar with a safety gap. It would 
help if someone could direct me to a diagram of one. 
Thank you for your help,