heh. i remember reading that this was called a gratuity awhile back. that and several other notable jargon used by the military are often jarring. technically, it works with the definition give at dictionary.com, http://dictionary.reference.com/browse/gratuity, and apparently originated with the British military.
But reading the definition where it says given "without claim or demand" and "without claim or obligation," I couldn't help but be reminded of a passage in _Nickle and Dimed_ where Ehrenreich remarks on the donuts given to the employees at Merry Maid. They were gratuities given "without claim, demand, or obligation" and, unlike a pay raise or benefits, could very easily be taken away whenever budgets got tight. Of course, pay can be lowered and hours reduced, and benefits have certainly been taken away, but it's a lot harder than simply ending the practice of daily donuts.
-- http://cleandraws.com Wear Clean Draws ('coz there's 5 million ways to kill a CEO)