An equivalent diameter for a particle defined as the physical diameter of a smooth solid sphere (of density 1 gram/cm³) that has the same terminal settling velocity in still air (under standard laboratory conditions) as the particle in question.

A relatively time-stable two-phase system consisting of finely-divided particles (that can be solids or liquids) suspended in a gas (which is usually air). Aerosol particles typically range in diameter from 0.001 to 100 μm.

A microorganism or a toxin derived from a microorganism that causes human disease and is used to harm people, or to elicit widespread fear or intimidation, for political or ideological goals.

A drug, biological product, chemical, or other therapeutic technology that prevents or treats an illness caused by a bioterrorism agent.

The amount (for bioaerosol particles this could be number, mass, viable units, or another metric related to biological effect) of an agent normalized to some property of the biological target (which could be mass, surface area or other descriptor of an individual, organ, or tissue). For example: mg of particles deposited in the subject; μg of particles deposited in the respiratory tract; μg of particles in the tracheobronchial region; or number of viable organisms in the alveolar spaces of the lung.

Geometric standard deviation - A measure of dispersion for a log-normal distribution that is analogous to the standard deviation for a normal distribution. The GSD is the ratio of the 84.13 percentile to the 50 percentile.

Mass median aerodynamic diameter - For aerosols, the MMAD equals the particle diameter at which particles larger than the MMAD contribute half of the collected mass and particles smaller than the MMAD contribute the other half.