The red bar on the left hand side of a patient appointment in the calendar view indicates that an appointment has not yet been recorded. Recording an appointment is a way of marking an appointment as complete, and starting the process of creating a charge. The red bar indicates that a patient has not been billed for this appointment. The details of the appointment, such as any payments, have not carried over to the patient's billing account. 

Marking the appointment as complete will start the charge creation process and remove the red bar. By default, accepting a payment from the calendar view in the scheduler will also record the appointment (if your practice has requested to turn the "Receipt Book" feature on, accepting payment will no longer automatically record an appointment.)

The patient has a co-pay that is due at the time of service. To see where this information is pulled from go to Persons and Institutions | Patients | Select a Patient | Demographics tab | Copay

An appointment note has been attached to the appointment. To see where this information is pulled from go to Scheduler | Calendar. Double-click an appointment and click the Appointment tab | Appointment Note

This is a recurring appointment. To edit this setting go to Scheduler | Calendar. Double-click an appointment and click Edit Recurrence

  This instance of a recurring appointment series has been edited. To see this setting click on Scheduler | Calendar. Double-click an appointment and revise "Start Time"/"End Time"
The patient has been checked in

The documentation for this session has not been started

The documentation for this session has been started, but it has not been signed

The documentation for this session has been signed

The documentation for this session has been skipped