What is 18th letter greek alphabet?

The 18th letter of the Greek alphabet is Rho (Ρ, ρ).

• It corresponds to the Latin letter R.
• In the system of Greek numerals, it has a value of 100.
• In modern Greek, it represents a voiced alveolar trill /r/.

It is used in various fields including:

• Physics: As a symbol for density, resistivity, and charge density.
• Statistics: As a symbol for correlation coefficient.
• Mathematics: As a symbol for polar coordinate systems particularly the radius.
• Finance: As a symbol for sensitivity of an option price to changes in the risk-free interest rate (see Greeks).