volatile organic compounds (VOCs): any compound of carbon, excluding carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, and ammonium carbonate, which participates in atmospheric photochemical reactions or whose composition makes it possible for them to evaporate under normal indoor atmospheric conditions of temperature and pressure. Sources: 40 CFR 51.100(s) and EPA VOCs Definition.
EPA notes that information about VOCs present at low concentrations normally found in indoor air is highly dependent on how the VOCs are measured. The range of VOC measurement methods and analytical instruments is large, and none can measure all VOCs. Therefore, marketing claims regarding VOCs should be substantiated with a description of how the VOCs were measured so that a professional may correctly interpret the results. EPA states that without such a description, the statement would have little practical meaning.
Source: EPA: An Introduction to Indoor Air Quality (IAQ).