Dividends (either in cash or in shares) are paid by many companies to its shareholders, most often on a quarterly basis. Why should options traders care about dividends? Dividends are part of the options pricing model, and so that alone makes them relevant. But the real answer is that dividends can impact option price movement much like the Greeks do. If you want a better handle on why options prices change, you'll need to watch your Greeks and any upcoming dividends on the underlying.
Let's go back to cost-to-carry for a moment. As stated earlier, rho helps an investor evaluate the opportunities and risks of interest rate changes on an option. The other factor impacting cost-to-carry is whether or not the stock pays a dividend. If an investor owns stock, carry costs can be determined using interest rates. However if the stock pays a dividend, the carry cost is reduced by the amount of the dividend the investor receives. Think of the interest cost as money going out, and the dividend as money coming in.
Because of this relationship, changes in dividends (increases, decreases, or the addition or elimination of them) will affect call and put prices. Since they somewhat counteract interest costs, they affect prices in the opposite manner as rho. Increasing dividends will reduce the price of calls and boost the price of puts. Decreasing dividends will have the reverse effect _ call values go up and put values go down.
Just as the passage of time affects all the Greeks, it also affects dividends. The more time to expiration, the more quarterly dividends may occur in the same period. So any change in a dividend will have a greater effect on longer-term options than shorter-term contracts.