$\psi$ — Psi

Lowercase psi (ψ) is the standard symbol for the quantum wave function — the mathematical object whose squared magnitude gives the probability of finding a particle. In fluid dynamics it denotes the stream function.

SI unit: m^(−3/2) (3D wave function normalization)

Used in

• Schrödinger equation for ψ(x,t)
• Born rule: probability density = |ψ|²