For requirements, scripts, incidents and script assignments type relates to the associated "Type" picklist.
For Automated tests and automated test assignments the Type field searches the type of automated test (which relates to the tool that produces it i.e. QTP, RFT, Selenium etc.)
Available values depend on the options available in the Type picklist in Enterprise Tester, for example:
Type = "Smoke Test"
To find all test scripts in project Testing with a type of "UAT":
EntityType = Script AND Project = Testing AND Type = UAT