Rho is a measure of how much the price of an option will change in relation to a change in the interest rate. Rho is often expressed as a decimal, and represents the change in the value of an option for every 1% change in interest rate.

For example, if an option has a rho of 0.01, that means that for every 1% increase in interest rate, the option's price will increase by $0.01. Conversely, for every 1% decrease in interest rate, the option's price will decrease by $0.01.

Rho is particularly important for options traders because interest rates are an important factor in options pricing. Higher interest rates make it more expensive to hold options positions, as options buyers are required to pay more to borrow money to buy them. As a result, options with higher interest rates will generally be less expensive.

Rho is also important for managing a interest rate neutral position, as it measures the rate of change of interest rate, it helps traders to adjust their positions accordingly to keep them interest rate neutral.

Rho is not constant, it changes as the underlying price changes, volatility changes and time passes. It is highest for long-term options and decreases as the options goes closer to expiration.

In summary, Rho is a measure of how much the price of an option will change in relation to a change in the interest rate. It is important for options traders to understand and monitor Rho when managing their positions, as interest rates are an important factor in options pricing.