It occasionally appears in optical character recognition (OCR) errors from archived newspapers, such as the Weirton Daily Times , where it is a misreading of unrelated text or numbers.
In technical specifications like HL7 Terminology , "47mp4" is used as a code representing the MP4 Video media type. such as the Weirton Daily Times
If you provide the context, I can give you a more specific answer about what it means for your device or project. Weirton Daily Times Archives, Apr 23, 1959, p. 16 such as the Weirton Daily Times