From IVoM:

mathematical relationship between quantities in a given system of quantities, independent
of measurement units
EXAMPLES

• a) Q ₁ = ζ Q ₂ Q ₃ where Q ₁ , Q ₂ , and Q ₃ denote different quantities, and where ζ is a numerical factor.

• b) T = (1/2) mv ² , where T is the kinetic energy and v the speed of a specified particle of mass m.

• c)  n = I·t / F where n is the amount of substance of a univalent component, I is the electric current and t the duration of the electrolysis, and where F is the Faraday constant.