See <<form factor>>

The ratio of the 60-decibel bandwidth of a bandpass filter to the 3-decibel bandwidth.

The quotient of the area of a sphere equivalent to the volume of a solid particle divided by the actual surface of the particle; used in calculations of gas flow through beds of granular solids.

For a lens, the quantity (R₂ + R₁)/(R₂ - R₁), where R₁ and R₂ are the radii of the first and second surface of the lens. Also known as Coddington shape factor.