Cancel an appointment, or mark a no-show

Open the appointment.

Cancel is for a visit that is not happening. It asks "Cancel appointment?" first, then confirms with "Appointment canceled".

No-show is for a client who did not turn up. It asks "Mark as no-show?" first.

Keep them separate rather than cancelling everything. A no-show is a fact about the client that you will want later, when you are deciding whether to ask that person for a card at booking.