A relational symbol indicating proportionality between quantities, commonly used in physics and mathematical equations.
Examples
Direct proportionality relationship
F \propto m \text{ (force is proportional to mass)}
Physical law relationship
V \propto \frac{1}{P} \text{ (Boyle's Law: volume proportional to inverse pressure)}
Probability density function
f(x) \propto e^{-x^2/2} \text{ (up to normalization)}