The Type of Service Reference is an older Reference in Builds 6.1 and earlier. It is a set list of all Types of Services that can be used in the drop down in the New Charge window on all types of MacPractice other than DDS.
In Builds 7.0+, this Reference has been removed, but the Types of Service are still accessible from the New Charge window in the Ledger, and References > Fee Schedule.
Types of Service, when selected on a Charge, will impact Box 23 of a CMS Claim form. Refer to the link for more information.