Definition for Volatile Organic Compounds (VOC)
VOCnote1, means any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical reactions. This excludes any such organic compounds which have been determined to have negligible photochemical reactivity (i.e. less than or equal to ethane's reactivity).
See Title 40 CFR 51.100 of https://www.gpo.gov/fdsys/pkg/CFR-2015-title40-vol2/xml/CFR-2015-title40-vol2-sec51-100.xml (revised as of July 1 2015) or the latest update.