(law,finance) A payment representing a fraction of the price of something being purchased, made to secure the right to continue making payments towards that purchase.
(by extension) Any initial commitment signifying an intention to carry out a larger future commitment, even though no legal rights or obligations are secured.
After decades of empty rhetoric, that's the down payment that we need on energy independence.
2009 April 4, Barack Obama, NATO summit
These commitments of troops, trainers, and civilians represent a strong down payment on the future of our mission in Afghanistan and on the future of NATO.
2022 March 9, Ben Jones, “RAIL Supplement: Return Ticket”, in RAIL, number 952, page 26 (supplement):
After all, when you buy a car, you're making a large down payment on future journeys - buying an annual rail pass or railcard should be no different.