According to legend, Jewish freedom-fighters holding secret meetings while plotting against the Syrians, pretended they were merely gambling.
Back then, people gambled with a top – called a dreidel in Yiddish – spinning it and letting it fall to see what letter appeared on top. That is why we play dreidel games at Chanukah; it's also why we hand out gelt ("coins"), either real ones or those made of chocolate.
Playing the game is simple.
On each side of the dreidel is a Hebrew letter, which stands for each word of the sentence, "Nes Gadol Hayah Sham," translated as "A Great Miracle Happened There!"
(In Israel, the four letters on the dreidel – nun, gimmel, hey and shin – stand for "A Great Miracle Happened Here!")