volotile organic coimpounds. Basically the amount of bad stuff evaporating into the air and that you will breath when applying the substance. I am not sure how it fits into formaldyhide as I only know about voc ratings of tile and grout sealers
Volatile organic compounds (VOCs) refers to organic chemical compounds which have significant vapor pressures and which can affect the environment and human health. VOCs are numerous, varied, and ubiquitous.