- A manner of describing the strength of a field. It may be expressed, for instance, as the concentration of lines or force, or the rate of flow of a quantity passing perpendicularly through a given area.
- A quantitative measure of the strength of a magnetic field present within a magnetic medium. It is the number of lines of flux per cross-sectional area of a magnetic circuit, and its SI unit is the tesla. Also called magnetic flux density, magnetic induction (1), or magnetic displacement.
- A vector quantity pertaining to the charge displaced by an electric field within a given medium. It is equal to the electric field strength multiplied by the permittivity of the medium. It is usually expressed in coulombs per square meter. Also called by various other names, including electric flux density, electric induction, or electric displacement.