A dividend is a cash payment to all shareholders.
In the game dividends are paid each month, and are thus regular dividends. In the real world companies sometimes declare special dividends. A Stock Split is also a special dividend, but one where shares are issued, but no cash.
By taking the annual dividend and dividing by the stock price the Yield of a stock can be calculated. This shows the amount of dividend payment that a shareholder will receive for each $100 in stock purchased. Thus a 3% dividend will result in a annual payment of $3 for each $100 of stock a shareholder owns. The higher the yield, the higher the payment the shareholder will receive.
See Also: Wikipedia Dividend