$\kappa$ — Kappa

Lowercase kappa (κ) denotes thermal conductivity — how well a material conducts heat. It also appears as curvature in geometry and as an alternate spring-constant symbol.

SI unit: W/(m·K) (as thermal conductivity)

Used in

• Fourier's law of heat conduction q = −κ∇T
• Curvature of a path in kinematics