Option Greeks (Delta, Gamma, Theta, Vega, and Rho) are parameters in the formula used to price option premiums, that is the Black-Scholes option pricing formula that was invented in the early 70's.
Confused? Bla Bla Bla is the first thing that comes to my mind when I read statements like the one above.
Let's me state the above in another way, Option Greeks are parameters used to determine what the price of a stock option will be given a $1 move in the stock price.
There are 5 components that make up Option Greeks and they are "If/then" in nature.
For instance, if the price of stock ABC goes up $5 then my stock option will be worth $X.
Learning how to trade stock options is hard enough and when you hear terms like Delta, Gamma, Theta, Vega, and Rho it discourages you from learning further because it makes options trading seem hard.
Let me walk you through the 5 Option Greeks

1. Delta is a measurement of how much an options price will change if the underlying stock moves up or down $1.
   00.
   
2. Gamma measures how much the Delta will increase/decrease for every dollar the stock moves.
   For instance, Gamma is 1.
   2 and Delta is 50, this means that if the stock moves up in value by $1 Delta will increase from 50 to 51.
   2.
   
3. Theta lets you know how fast your stock option will lose value as the days go by (it approaches expiration).
   A Theta of.
   05 means that the time value component of the option loses $0.
   05 every day that passes.
   The rate of price decay speeds up as the option approaches expiration.
   
4. Vega lets you know how much the stock option price will change as the volatility of the underlying stock changes.
   
5. Rho is an estimate of how much the stock option price will change when interest rates change.
   Rho is not used as often as the other 4, as interest rates don't change very often.
   

Essentially option Greeks help you determine how certain factors will affect the price of your stock option.
Depending on the trader's objectives and the situation in the market, the trader can be very picky and choose options on the stock in question, options that make the most money and offer the minimum possible risk.
Options parameters may seem overwhelming in the beginning but as you become more familiar, things will sink in and you'll be able to recognize their profit potential.
Option writers (option sellers) tend to use option greeks fairly frequently as they will determine which stock option will yield the most profit in the shortest amount of time.