What does the “Thumb” mean on an appointment?

When an Appointment is booked for a member/customer/client, you see a thumb just next to their name. It indicates confirmation. You will see the "Thumb" as shown in the below screenshot

You can click on Calendar >> click on the appointmet that you want to see. You will be able to see the screenshot as above.

When there are more than one customer booking the appointment for a particular service then you will not see the "Thumb" icon. You will see a "check" as shown in the below screenshot: