...is the name of the policyFile located in the C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\config directory.
The individual wss_custom_wss_minimaltrust_GUID.config files will have different ending GUIDs, like this:
wss_custom_wss_minimaltrust_1fed96fb-db74-4076-9a48-d8a73f8a9b9f.config
wss_custom_wss_minimaltrust_520cb066-1535-4126-8551-3324419c025c.config
wss_custom_wss_minimaltrust_16cea51a-9c26-4dd2-bda5-0a0695605390.config