1. Rho (upper case Ρ, lower case ρ) is a letter of the Greek alphabet. See Rho (letter).
2. The lower-case letter ρ is used as the symbol for the radius in a polar coordinate system in mathematics.
3. The lower-case letter ρ is used as the symbol for the density of a material in physics.
4. The lower-case letter ρ is used as the symbol for the resistivity of a material in physics.
5. The lower-case letter ρ is used as the symbol for the Rho factor protein in RNA transcription termination.

Rho is also the name of a town near Milan, in Italy