Christmas club

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A savings account, as in a bank, requiring periodic deposits to ensure money for shopping at Christmas.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun banking A type of savings scheme in which a person pays in money through the course of a year and gets back a total at around Christmas time ready to buy gifts or treats for Christmas. Such schemes have been run by banks and retailers and generally only involve fairly small amounts of money.