DEFINITION of 'Greeks'
Dimensions of risk involved in taking a position in an option (or other derivative). Each risk variable is a result of an imperfect assumption or relationship of the option with another underlying variable. Various sophisticated hedging strategies are used to neutralize or decrease the effects of each variable of risk.
INVESTOPEDIA EXPLAINS 'Greeks'
Neutralizing the effect of each variable requires substantial buying and selling and, as a result of such high transactions costs, many traders only make periodic attempts to rebalance their options portfolios.
With the exception of vega (which is not a Greek letter), each measure of risk is represented by a different letter of the Greek alphabet:
Δ(Delta) represents the rate of change between the option's price and the underlying asset's price  in other words, price sensitivity.
Θ(Theta) represents the rate of change between an option portfolio and time, or time sensitivity.
Γ(Gamma) represents the rate of change between an option portfolio's delta and the underlying asset's price  in other words, secondorder time price sensitivity.
ϒ(Vega) represents the rate of change between an option portfolio's value and the underlying asset's volatility  in other words, sensitivity to volatility.
ρ (Rho) represents the rate of change between an option portfolio's value and the interest rate, or sensitivity to the interest rate.

Zomma
An options greek used to measure the change in gamma in relation ... 
Ultima
The rate at which the vomma of an option will react to volatility ... 
Gamma
The rate of change for delta with respect to the underlying asset's ... 
Beta
A measure of the volatility, or systematic risk, of a security ... 
Lambda
The ratio of the percentage change in an option contract's price ... 
Vega
The measurement of an option's sensitivity to changes in the ...

Options & Futures
Getting To Know The "Greeks"

Options & Futures
Options Basics Tutorial

Options & Futures
Trading The QQQQ With InTheMoney Put ...

Options & Futures
Option Spread Strategies