A collection of money by a political official or administration that is used to make payments for various services. Though slush funds may be used for legitimate purposes, such as paying state employees, the term is generally used to describe money that is not properly accounted for and is being used for personal expenses and political payoffs. Money raised for political campaigns has come under increasing public scrutiny to ensure that it is not misused.
In politics, money used for shady enterprises like buying votes, bribing officials, etc: the use of slush funds to defeat selected victims
[1839+; fr the armed forces and especially nautical practice of selling grease and other garbage to accumulate a fund to buy little luxuries for the troops or crew]