food stamp

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

• noun A stamp or coupon, issued by the government to persons with low incomes, that can be redeemed for food at stores.

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

• noun A stamp or similar paper document (e.g. coupon) issued to be exchanged in shops or storage facilities for food, or (by extension) for other essential provisions, notably in a rationing system or as a non-financial form of welfare benefit

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a government-issued stamp that can be used in exchange for food