This post defines common IAQ terms (adapted from the U.S. Environmental Protection Agency (EPA)) and some abbreviations used in many of the modules. Text in square brackets  has been added by the authors of this document.
Air changes per hour (ACH): the amount of air in a building that leaks out or is removed by a fan and is replaced by outdoor air, usually listed as a fraction of one air change per hour, such as 0.35 ACH. [ACH is sometimes referred to as air exchange rate or AER.]
ASHRAE: American Society of Heating, Refrigerating and Air-Conditioning Engineers.
Building envelope: [the] elements of the building, including all external building materials, windows and walls that enclose the internal space.
Biological contaminants: agents derived from, or that are, living organisms (e.g., viruses, bacteria, fungi, and mammal and bird antigens) that can be inhaled and can cause many types of [adverse] health effects including allergic reactions, respiratory disorders, hypersensitivity diseases, and infectious diseases, also referred to as “microbiologicals” or “microbials.”
Carbon dioxide (CO2): a colorless, odorless, and tasteless product of combustion. All combustion processes and human metabolic processes are sources of CO2. Concentrations of CO2 from people are always present in all occupied buildings, and at concentrations normally found in buildings, CO2 is not a health hazard.
Carbon monoxide (CO): a colorless, odorless, and tasteless gas which results from [incomplete] com- bustion of fuels. It is often associated with combustion heating devices (e.g. boilers, furnaces) and auto, truck, or bus exhaust from attached garages, nearby roads, or parking areas. At moderate concentrations, angina, impaired vision, and reduced brain function may result. At higher concentrations, CO exposure can be fatal.
Formaldehyde: Formaldehyde is a colorless water-soluble gas. Due to its wide use, it is frequently considered separately from other VOCs. Materials containing formaldehyde include building materials, furnishings, and some consumer products. [It is also a by-product of combustion.] Formaldehyde has a pungent odor and is detected by many people at levels of about 100 parts per billion (ppb). Besides the annoyance, it also causes acute eye burning and irritates mucous membranes and the respiratory tract. [The risk of cancer associated with formaldehyde levels, sufficiently low to prevent irritation and inflam- matory responses, appears to be negligible (Health Canada, 2006)].
Fungi: any of a group of parasitic lower plants that lack chlorophyll, including molds and mildews.
HEPA: high-efficiency particulate arrestance [air] (filters).
IAQ profile: a base-line description of the features of a building structure, function, and occupancy that impact indoor air quality. A completed IAQ profile provides an understanding of the current status of air quality in the building and baseline information on the factors that have a potential for causing problems in the future. For more information about developing and using an IAQ profile, see Module 8 – Creating an IAQ Profile.
NBC: National Building Code of Canada. NFC: National Fire Code of Canada.
Off-gassing: the production of gases from the chemical deterioration of a substance over time, and the release of gases from materials into the air. [See VOCs]
Pollutant pathways: avenues for distribution of pollutants in a building. HVAC systems are the primary pathways in most buildings; however all building components interact to affect how air movement dis- tributes pollutants.
Radon: radon is a colorless, odorless, radioactive gas that occurs naturally in the environment [from the breakdown of uranium in soils and rocks]. Outdoors, its concentration is rendered negligible. But when it is emitted into an enclosed space, such as a building, it can accumulate to high levels and be a carcino- gen. [Exposure to high levels of radon has been associated with an increased risk of lung cancer.] Radon can seep from the ground into buildings through cracks and unsealed penetrations in the floor and walls abutting the ground.
Volatile organic compounds (VOCs): compounds that vaporize (become a gas) at room temperature. Common sources which may emit VOCs into indoor air include housekeeping and maintenance pro- ducts, and building and furnishing materials. In sufficient quantities, VOCs can cause eye, nose, and throat irritations, headaches, dizziness, visual disorders, memory impairment; some are known to cause cancer in animals; some are suspected of causing, or are known to cause, cancer in humans.
For a more complete list of terms, see http://www.epa.gov/iaq/glossary.html
You can find this post, as well as more information in Module 1 – Introduction to Indoor Air Quality (IAQ)