Ticket services is a feature in ClearCRM that allows your customer to select to what service/product this ticket is related when opening a new ticket.
Eq.
Product/Service 1
Product/Service 2
Product/Service 3
When your customer will open the ticket the admin will know that this ticket is related to specific service.
You can easily enable / disable this option from Setup->Settings->Support.
To create a new ticket service navigate to Setup->Support->Services.