The "Greeks"

Trying to predict what will happen to the price of a single option or a position involving multiple options as the market changes can be a difficult undertaking. Because the option price does not always appear to move in conjunction with the price of the underlying asset, it is important to understand what factors contribute to the movement in the price of an option, and what effect they have. Options traders often refer to the delta, gamma, vega and theta of their option positions. Collectively, these terms are known as the "Greeks" and they provide a way to measure the sensitivity of an option's price to quantifiable factors. However it's important that you realize the Greeks don't determine pricing, they just reflect what could happen in pricing changes for moves in stock, implied volatility, etc.