As a photographer, my contract states that the Client must pay 50% upfront, 25% 1 month before the shoot, and 25% after completion.

The 50% payment is non-refundable. This payment covers my reservation to secure the booking with the client and any expenses, such as rentals, permits, props, and hires.

What would you call this initial 50% payment? - Retainer, Deposit (non-refundable), or a Reservation Fee