Any of various mathematical objects occurring in or derived from the work of Pfaff on differential equations. Originally: specifically (A. Cayley's term for) a function involving permutations arising from this work.
Of or relating to (mathematical objects occurring in) the work of Pfaff; specifically designating a differential equation of the form f ₁ d x ₁ +…+ f ₙ d x ₙ = 0, where each f i is a function of the variables x i.
Mid 19th century; earliest use found in Arthur Cayley (1821–1895), mathematician. From the name of Johann Friedrich Pfaff, German mathematician + -ian.