petty cash

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

• noun A small fund of money for incidental expenses, as in an office.

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

• noun a small amount of cash kept by a company, used for low-cost immediate expenditure

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

• noun a small fund of cash that a firm keeps for the payment of incidental expenses