Delta refers to the relationship between the option's price and the Underlying, for calls, Delta is positive, for puts, Delta is negative. Gamma is the rate at which Delta is changing, a higher Gamma means Delta will fluctuate more based on changes to the Underlying. Vega is the sensitivity of the option price to changes in the Volatility of the Underlying. Theta measures the effect of time on the value of the option. Rho is the sensitivity of the option to changes in interest rates, this usually has the lowest impact on the price of an option than the other Greeks.