Final answer:
Appointments entered in a second column beside regular appointments are referred to as double booking or a waiting list, depending on the situation's context and intent.
Step-by-step explanation:
When appointments are entered in a second column beside the regularly scheduled appointments, this is often referred to as double booking or creating a waiting list. In the context of schedule management or calendar organization, double booking can imply that two appointments are scheduled at the same time, which may or may not be intentional depending on the situation. A waiting list, on the other hand, is used to schedule additional clients who can be called in case of cancellations or no-shows, thereby optimizing the schedule efficiency.