What is the context? Where do you see this filter?what does this mean?
I would expect in this case it is denoting magnetic flux because the symbol is often paired with a "B" in those cases (though most often it is a subscript):The lower-case letter φ (or often its variant, ϕ) is often used to represent the following:
The upper-case letter Φ is used as a symbol for:
- The golden ratio1.618033988749894848204586834... in mathematics, art, and architecture.
- Euler's totient function φ(n) in number theory; also called Euler's phi function.
- The cyclotomic polynomial functions Φn(x) of algebra.
- In algebra, group or ring homomorphisms
- In probability theory, ϕ(x) = (2π)−½e−x2/2 is the probability density function of the normal distribution.
- In probability theory, φX(t) = E[eitX] is the characteristic function of a random variable X.
- An angle, typically the second angle mentioned, after θ (theta). Especially:
- The argument of a complex number.
- The phase of a wave in signal processing.
- In spherical coordinates, mathematicians usually refer to phi as the polar angle (from the z-axis). The convention in physics is to use phi as the azimuthal angle (from the x-axis).
- One of the dihedral angles in the backbones of proteins in a Ramachandran plot
- Internal or effective angle of friction.
- The work function of a surface, in solid-state physics.
- A shorthand representation for an aromatic functional group in organic chemistry.
- The fugacity coefficient in thermodynamics.
- The ratio of free energy destabilizations of protein mutants in phi value analysis.
- In cartography and navigation, latitude.
- In combustion engineering, fuel–air equivalence ratio. The ratio between the actual fuel air ratio to the stoichiometric fuel air ratio.
- A sentence in first-order logic.
- The Veblen function in set theory
- Porosity in geology and hydrology.
- Strength (or resistance) reduction factor in structural engineering, used to account for statistical variabilities in materials and construction methods.
- The symbol for a voiceless bilabial fricative in the International Phonetic Alphabet (using the straight line variant character)
- In economics, this is usually an additive term.[clarification needed]
- In flight dynamics, the roll angle.
- In philosophy, φ is often used as shorthand for a generic act. (Also in upper-case.)
- In perceptual psychology, the phi phenomenon is the apparent motion caused by the successive viewing of stationary objects, such as the frames of a motion picture.
The diameter symbol in engineering, ⌀, is often incorrectly referred to as "phi". This symbol is used to indicate the diameter of a circular section; for example, "⌀14" means the diameter of the circle is 14 units.
- The golden ratio conjugate −0.618... in mathematics.
- The magnetic flux and electric flux in physics, with subscripts distinguishing the two.
- The cumulative distribution function of the normal distribution in mathematics and statistics.
- In philosophy, Φ is often used as shorthand for a generic act. (Also in lower-case.)
- The number of phases in a power system in electrical engineering, for example 1Φ for single phase, 3Φ for three phase.
- A common symbol for the parametrization of a surface in vector calculus.
- In Lacanian algebra, Φ stands for the imaginary phallus and also represents phallic signification; -Φ stands in for castration.