Image credit Gary
I believe the acronym stands for "Small Personal Items."
Normally on backcountry runs I use a 1 or 2 bottle pack, with a compartment that can also carry some food, Epipen, matches, etc. But on very short trail runs, or on road runs, this SPIBELT fits the bill perfectly.
It is made of some stretchy material that'll easily hold my iPhone 5, my Epipen, money, and even some keys. The waist sizing is fully adjustable so that you can crank it as tight as is required to eliminate the weight-dependent bouncing of the contents.
By the way, I have no financial interest in endorsing this product. It simply works, and works extremely well. It is easily found online.