Why do people play with a dreidl on Hanukkah?

Dreidl means "top" (the kind that spins) in Yiddish. The game was devised to teach children about the story of Hannukah. The four Hebrew letters ('nun' 'gimmel' 'hey' and 'shin') on each side of the top are an acrostic for the phrase "Nes Gadol Hayah Sham" - meaning "A great miracle happened there". In Israel, the last letter is 'pey' for "Po" - "here" - because the Hannuka story took place in Israel.