A customary gift for Jewish children on Hanukah. The word gelt comes from Yiddish, meaning "money". Gelt are usually chocolate coins, wrapped in gold tinfoil (unless it is homemade). Hanukah gelt can also be real coins.
An explanation of the gelt custom as told by Rabbi Dovid Cohen:
"The Talmud states that even a very poor person must light Hanukah lights, even if he can't afford it. A person with no money is required to go 'knocking on doors' until he collects enough to buy at least one candle for each night of Hanukah."
"The Torah concept of charity - tzeddakah - requires us to help the recipient in the most dignified manner possible. Therefore, the custom arose to give gifts of money during Hanukah so that someone who needs extra money for Hanukah candles can receive it in the form of Hanukah gelt."