Rho
The rate of change of an option price with respect to changes in the risk-free interest rate.
Explanation
Rho measures sensitivity to interest rate changes. It is typically the least impactful Greek for short-term options but becomes significant for LEAPS and in high-interest-rate environments. Calls have positive rho (benefit from rising rates); puts have negative rho.
Example
A LEAPS call with rho of 0.15 would gain $0.15 in value for each 1% increase in interest rates.