First thread--What is "Stabilizer Level?"

[vernrose]

I was reading th e page in PoolSlutions on Avoiding Algae in Chloinated Swimming Pools. We have both. The tables they show for chlorine levels are dependent on water temperature and the "Stabilizer Level." I understand the water temp. but not the stabilizer level. What is it and how do you measure it. Thanks for any guidance.
Vern