Ticket Sub-Statuses can be added to the Core Statuses (Awaiting Agent/Awaiting User/Pending/Resolved) that are available to Tickets in order to better define what state a Ticket is currently in.

Any Sub-Statuses that have been created by your Admins will be available for selection in the Status drop down field on the top right hand corner of the Ticket or next to the reply box when replying to a Ticket.

When you hover over the Core Status, the sub-status would appear as shown below:

In order to select a Sub-Status, you must first hover over the correct Core Status and the appropriate Sub-Statuses will appear.

The appropriate Core Status and Sub-Status will show when viewing the Ticket, and Sub-Status will show in the list of Tickets.

Sub-Statuses can also be used in  Follow Ups and other automation features in your helpdesk.