No-show fee
A no-show fee is an amount charged when a client misses an appointment without cancelling in time. It compensates for a chair that stayed empty and is usually collected from a card held or a deposit taken at booking.
Also called: missed appointment fee, late cancellation fee
What changes behaviour is the client knowing, at the moment of booking, that money is attached to the slot.
Most shops set the notice window at 24 hours and charge some fraction of the service price rather than all of it. The aim is to make missing an appointment cost something, not to punish someone whose car broke down.