From the online help search for RAD
Recorded Announcement Device (RAD) Greetings
(Embedded Voice Mail)
Overview:
This feature provides the ability to play greetings through a voice mail port (RAD port), eliminating the need for external tape machines or other audio-playing devices. RADs are commonly used to automatically answer incoming calls and deliver pre-recorded messages such as "All of our representatives are busy helping other callers, please continue to hold to maintain your call priority." When the RAD message finishes playing, the caller usually hears Music on Hold while waiting for an agent to become available. RAD messages may also give the caller information, which answers their questions, thus resulting in a 'good' abandoned call. They may also provide advertising or promotional information to callers while they're waiting for someone to take their call.