Orderable Item Dictionary
The Order Item Dictionary (OID) is the dictionary that holds a list of the unique Order entries. This is typically built based on the compendium from you primary vendor, but may also include other tests from your other vendors. Ultimately this is the list of Orders that the user will have the ability to Order from within TouchWorks (assuming they are set as Orderable and Users are allowed to order the test in the OID).
To learn more about building the OID please refer to V11 Order and Result Dictionary Build and Syncronization.