VOCs
If something smells, there's a good chance it's releasing VOCs (Volatile Organic Compounds). VOCs are compounds that contain carbon and come from a variety of sources - some good, and some bad. Check out the VOCs explained podcast for a discussion of some of the different types of VOCs.
VOCs are any compound that can volatilize (enter the gas-phase from a solid or a liquid) at room temperature and pressure. There are hundreds of compounds that qualify as VOCs. One way to identify VOCs is through smell. For example gasoline vapors, cleaning supplies, paints, bacon sizzling in a pan, plants, and perfume are all VOCs. Another term commonly used for VOCs is hydrocarbons. VOCs can also be formed by incomplete combustion (non-ideal, also producing CO).
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Reference Levels
Sources of VOCs
Currently, there is no standard set for VOCs, but studies have found that levels of several organics average 2 to 5 times higher indoors than outdoors.