Answer:
Grease payment
Explanation:
A grease payment is a payment made to a government official with the goal of expediting a transaction, process or request. It can be obtained through extortion from the government official, by voluntary contribution from the non-goverment official, or by mutual agreement, either explicit, or implicit.
In practice, it is essentially the same as a bribe, and the term could be considered a colloquial euphemism.